Saturday, March 11, 2017


Mandookya Upanishad--Cornerstone of Advaitaa Philosophy & Paancharaatra Theology
(Compilation for a Discourse by N.R. Srinivasan, Nashville, TN, USA, March 2017)

One has to go through 108 Upanishads or 32 important or at least ten major Upanishads on which Sankara and others have elaborately commented upon to   understand Brahman and meditate upon for salvation. If on the other hand if one masters Bhagavadgeeta besides which is essentially compendium of all Upanishads, contemplation on Mandookya Upanishad alone is sufficient for deliverance.  Rama expressed such an opinion on this short and deep Upanishad even before the deliverance of Bhagavadgeetaa to humanity. What makes this small Upanishad containing only twelve mantras so great? One of the four Mahaavaakyas (great quotes) of Upanishads “ayam atma Brahma” (The Self is Brahman) is found in the second mantra of this Upanishad. Even these twelve mantras are arranged in four Khandas (cantos). The contents of this Upanishad might have come from Brahmasootra 3-2-9: "Sa eva tu karmaanu-smriti-sabda-vidhibhyah"-- But, on account of the inevitability of the experience of Karma  and the remembrance of the fact that he is the same that has gone to deep sleep, and the scriptural statement that the   Sushupta alone wakes up and forms the injunction relating to final release, it becomes decided that the same person wakes up from "Sushupti"
 “Ayam aatma Brahma” of Mandookya Upanishad is from Atharvaveda, meaning “This Self or Aatma is Brahman”.  Here this statement gives the expression to the intuitive experience of the aspirant. This is identified as Anubhava-Bodha Vaakya in Vedanta.  Badarikasram Jyotir Math one of the four monasteries established by Sankara has adopted this Mahaavakya  as its motto. This Upanishad elaborates on four aspects of Supreme Being which are often cited in many Upanishads as Wakeful State, Dream State, Deep Sleep or Dreamless Sleep state and the last simply mentioned as fourth state being undefinable. These are again as Vaiswanara, Tejasa, Prajnya and the Fourth   expressed in Sanskrit as Tureeya. These are further referred as   A, U, M and half syllable contained in the divine syllable called Pranava and meditated upon as AUM. These four states are referred as Aniruddha, Pradyumna, Sankarshana and Vaasudeva. In Vishnusahasranama Vishnu is glorified as all-pervading Supreme Being and is referred as “Chaturvyuhah”. Thus in this Upanishad the characteristics of four vyuhas, the particular state to which they relate,  the mode  of contemplation on these four aspects of the Supreme Being and the great benefits one can derive  from such a meditation have been presented in an effective capsule form.  “In Bhajagovindam verse 24 Sankara says “Tvayi mayi cha anyatra ekah vishnuh’’—ultimately there is one Vishnu, in you, in me, and in everything. There is one all-pervasive lord, this Narayana alone. This is a very comforting vision. The very idea gives us such relief, that we are Vishnu, we are Narayana and we are limitless. Whether or not we are able to see ourselves as free or limitless today is a matter of our knowledge or experience, but the scriptures reveal this vision about us. We are told “tat tvam asi”--that thou art in Chandogya Upanishad; we are the limitless, that divine, or the ultimate Truth”-writes Swami Viditananda in his commentary on Bhaja Govindam.
No wonder this Upanishad has attracted the attention of great many gurus and scholars   among ten cardinal   Upanishads like Isavasyopanishad.
We walk through four states of Consciousness in our everyday life. We go through the initial three states of wakefulness, dream and deep sleep in which the mechanical nervous system rests and at the end of it reach a state of un-describable state called Turiya,   which is often translated roughly as temporary state of Bliss called Ananda. In fact it is hard to find exact translation of the word in any human language for this Aananda   which is hidden in the wisdom of Vedas.   Chandogya Upanishad describes Turiya  state as follows in 8.3.2—All the Jeevatmas go through the Supreme Lord day  in and day out during this fourth state but do not get or know that Brahman. It is just like walking on the gold mine happily without knowing it”.  Aananda is a temporary state of being with Brahman without realization. Though everyday all people in this world unite with Brahman and momentarily happy they do not know that they have united with Brahman because of their Karma. You now understand why it is difficult to describe the fourth state.
Vaayu Purana glorifies five war heroes of Vrishni family Sankarshana (Balarama brother of Krishna) Vasudeva (Krishna), Samba (son of Jambavati and Krishna), Pradyumna (son of Rukmini and Krishna) and  Aniruddha (son of Pradyumna). These human beings are deified in Bhagavata Tradition. The four heroes Sankarshana, Vasudeva, Pradyumna and Aniruddha are now regarded as emanations from Paravasudeva.  From Parvaasudeva emerges Vyuha Vasudeva (or Shadgunya vigraha, Bhagawan with six virtues; Lord Krishna from whom Sankarshana comes forth, a secondary emanation. From Sankarshana emanated Pradyumna and from Pradyumna Aniruddha. These four Vyuhas are associated with four states as described above.
Vaishnavites recite 24 forms classical forms of Vishnu in their daily prayers.  According to Pancharaatra doctrine (doctrine of four heroes deified with Paravasudeva constituting five aspects) each of the four Vyuha or primary emanatory forms of Vishnu bring fourth three other forms which are regarded as Vyuhaantara secondary emanation.  The twelve secondary emanations are together called murtyaantara or dvaadasa murtis. From these twelve secondary emanations eight other forms which are further manifestations from the four primary vyuha-murtis are produced bringing the total to 24 (4+12+8=24. Mandookya Upanishad gave birth to Pancharatra Samhitas which are the scriptures of certain Vaishnava sects of Hinduism.  The numbers of texts pertaining to these Samhitas are 250; of them Brihad Brahma, Iswara and Jnaanaamrita-saara Samhitas are noteworthy.
Mandookya Upanishad is considered as    basic to all the Principles of Vedanta and   the cornerstone to   Advaita Philosophy. An analysis of three states of Consciousness—Jaagrati, Swapna and Sushupti and linking them with the three letters A, U, M of the Pranava  syllable AUM  (akaara, ukaara, makaara and onkaara) and establishing Tureeya  (unexplainable fourth state) as the highest reality is the specialty of its message to spiritual seeker. To Vaishnavites it is the Cornerstone on which Pancharatra doctrine is framed.
The seer of this Upanishad seems to be the son of Mandookya   Maharshi.  In Aitreya Upanishad there is a reference to Mandookeya. Out of their Humbleness the great sages   who are authors of various   Upanishads did not openly reveal their authorship even though we come across the names of many sages both male and female in Upanishads.  According to Madhvacharya and his two followers, Thirtha and Srinivasa, Mandookya Upanishad was handed down by Varuna in the form of Frog (Mandooka). In fact Upanishads do not generally have an author and yet in our own weakness we try to discover an author for these great literary pieces.  Mandookya like Taittareya and Aitreya is in prose form.
Mantra 1: Past, present and future are forms of AUM, Omkara.
Mantra 2: Four steps of the union of Brahmana and AUM.
Mantra 3: First step Vaiswaanara described.
Mantra 4: Second step Hiranyagarbha Taijasa described.
Mantra 5: Third step blissful Praajnya described.
Mantra 6: Why is Brahman omniscient and God of all?
Mantra 7: Fourth step formless Brahman without qualities described.
Mantra 8: Three syllables A, U, M of Pranava.
Mantra 9: First Syllable A with Vaiswaanara associated.
Mantra 10: Second Syllable U with Taijasa associated.
Mantra 11: Third Syllable M with Praajnya associated.
Mantra 12: Knowing Brahman without syllable as fourth step.

No Upanishad starts without the Guru and the disciple sitting and chanting together the peace Invocation. Just before the study of the Upanishad, the Guru and the student pray invoking the best in them to come out by a full surrender to the mighty powers of an omniscient God-Principle.  Their invocation to Vedic Gods Indra, Vaayu, Sun etc. makes us remember that Rama, Krishna and such  other Puranic Gods are the products of a much later age. In the Vedic period, this study team knew only of the  five Great Elements and such other manifestations to be the Divine personalities, the Divines or Devatas. They are invoked here both by the guru and the disciple.
No peace invocation concludes without repeating thrice peace or invoking peace (Shanti mantra). These   three repetitions are addressed to the three groups in which all the probable obstacles in the study of scriptures can be classified. They are the   God-sent-(Aadi Daivika) such as lightning, thunder; Phenomenon (Aadi Bauthika) such as fire, floods, landslide etc.;   and Purely Subjective (Aadhyaatmika) such as, inertia, lack of faith insincerity and such others that arise from our own negativities or inner disturbances.
Om bhadram karnebhih   srunuyaama devaaha; bhadram pasyemaakshabhir-yajatraaah  sthirair-angais-tushtuvaagam sas-tanoobhih vyasema devahitam yadaayuh || swasti na indro vriddhasravaah; swasti naha poosha viswavedaah |  swasti nastaarkshyo arishtanemih; swasti noe brihaspatir-dadhaatu | |
 || Om saantih, saantih, saantih ||
O ye Gods! May we hear with our ears (always) what is auspicious; O Worshipful Ones, may we with our eyes see (always) what is auspicious. May we live the entire length of our allotted life hale and hearty, offering our praises (unto Thee)! May Indra, the ancient and famous, Sun (Pusan) the all-knowing, the Lord of swift motion(Vaayu) who saves us from all harms and Brihaspati who protects the spiritual wealth in us—bless us (with intellectual strength to understand the scriptures and the heroic heart to follow the teachings). Om Peace be; peace be; peace be.
[Such Shanti Mantras are often times employed as Mantrapushapas (Spiritual flower offering) during the worship of the Lord in temples and at homes]

Mantra 1 Aum ity-etad-aksharam ida(ga)m sarvam | tasyopa-vyakhyaanam bhootam bhavad-bhavishyad-iti sarvam-onkaara eva | yaccha-anyat-trikaala-ateetam tadapy-onkaara eva ||
All this is syllable AUM.   A clear exposition of this fact follows. All that existed in the past  that exists in the present and what will become in the future is verily AUM; whatever is beyond these past, present and future is also AUM.
The four parts of Pranava [A (beginning), U (continuous), M (closing) and the nasal half sound] correspond to the four aspects (Vyuhas) of Brahman—Aniruddha, Pradyumna, Sankarshana and Vasudeva and they in turn correspond to Viswa, Tejasa, Praajna and Tureeya.  This is often referred as Paada Chatushtaya or Chaturvyuha in Pancharatra Theology.  All things either limited by time or not limited by time or verily the sound of AUM or Brahman alone. This here refers to manifested world. AUM  is not only what is past, present and future but also what is beyond past, present and future.
Mantra 2 Sarva(ga)m hyetad-brahma-ayam-aatmaa brahma | so-ayamaatma chatush-paat ||
All this is verily Brahman. Self (Aaatman) is Brahman. Aatman has four quarters or phases of consciousness.
Omkaara is Brahman. Brahman is Self in all.  So the individual soul or Atman is Brahman.  This Atman has four quarters (parts).
In the second canto Mandookya upanishad describes the three quarters as Vyswanara, Tejasa and Praajna which corresponds to the three divine Vyuhas Aniruddha, Pradyumna and Sankarshana, representing  three states of Wakeful, Dream and Deep sleep—Jagriti, Swapna and sushupti.  Though each quarter has been expounded with certain definite characteristics, the three quarters are to be reflected in the same way. Viswa is the gross body Taijas subtle body and Praajna is the causal body. These three together constitute the Microcosm.  At Macrocosm or Universe level,  Viswa is designated as  Virat,  Taijasa  as Hiranyagarbha and Prajna as Iswara. Gross body is the food sheath; Vital sheath, Mental sheath and Intellectual sheath together constitute the subtle body; and Bliss sheath is the causal Body.

Mantra 1: Jaagaritasthaano bahih prajnyah saptaanga ekonavimsati-mukhah sthoolabhug-vaiswaanarah prathamah padah //
 The first quarter is Vyswaanara who is the ordained of the waking state, whose consciousness relate to  external things, who is possessed with seven limbs like the sun, the air and the earth and who has eighteen mouths ( an instrument of consumption) such as motor organs and sense organs and who enjoys gross things.
Chhandogya Upanishad describes seven limbs as follows: The Heaven is the head; the Sun is the eye; Air is the vital force; Space is the trunk or the middle part; Water is his bladder and Earth is his feet. The nineteen mouths are; Five sense organs (Jnanedriyas), five motor organs (Karmendriyas), Five vital force (pancha praanas) and four Antahkaranas-mind, intellect, ego and consciousness (chitta). In this State one lives with all things focused   outward, aware of the outside world only. Vaiswanara means one who leads all beings of this world. Presiding principle over wakeful state is called Vyswanara  that is   Aniruddha.
Mantra 2: Swapnasthaana-antah prajnyah saptaanga ekonavimsati-mukhah praviviktabhuk-taijaso dwiteeyah paadah ||
Taijasa is the second quarter. This sphere of activity is individual’s dream state. It cognizes internal objects and his consciousness is turned on internal world of objects. He too is possessed of seven limbs and nineteen mouths and enjoys subtle objects (of mental world).
Objects experienced in dream state are not the same as in the wakeful state. This state corresponds to Pradyumna.  Pradyumna is called inner consciousness (antahprajnya). The dream state created by the Lord exists as long as dream lasts. The objects of the dream are experienced only by the Self or Jeevaatman  for the duration of   the dream and so the presiding deity of the dream is called Tejasa and that is Pradyumna.  In this state one lives with all senses focused inwards enacting a drama of past deeds and present desires, factual or imaginary.
Mantra 3: Yatra supto na kanchana kaamam kaamayate na kanchana swapnam pasyati tat-sushuptam |sushuptasthaana ekeebhootah prjnyaana-ghana  eva-aanandamayo hyaanandabhuk-chetomukhah praajnyas triteeyah paadah ||
The Prajnya is the third quarter where the Jeevaatman (in its sookshma sareera) the sleeper    has no dreams or wants. He is the very embodiment of cognition, a mass of Consciousness. e prepares the Jeeva to experience He
 It prepares the jeeva for the last stage of Aananda (a state of temporary Sayujya or oneness with Brahman) roughly called as Bliss state of deep asleep. In this state Jeeva  (Self) is not overcome by the defects of desire and others and it does not experience dreams.  Lord himself is in his state of Sushupti as a solid mass of consciousness and He causes the Jeeva (Self) to experience bliss of deep sleep.    He who is known through pure mind, who is of the form of Bliss and consciousness, is called Sankarshana. There is neither   individual mind nor separateness in this state and it opens the gateway to for the projection of consciousness into the other two planes of consciousness the dream and the waking.
When we have transcended both the states of waking and dream, we will be in a state called the dreamless deep sleep, and in that state the Consciousness in us is illuminating neither the gross objects of the outer world nor the subtler objects of the mental zone. There, in this deep sleep state, the entire consciousness in us seems to have collected together in us and crystallized into one mass of awareness. At this state of experience, our entire consciousness has become a homogeneous mass of awareness (prajnyaanaghana.)
Mantra 4: Esha sarveswara esha Sarvajnya esho-antaryaamyesha yonih sarvasya prabhavaapyayau hi bhootaanaam  ||
This is the fourth quarter (fourth aspect of Self as it were) different from the other three. He is the Lord of all. This Self is omniscient; this is the inner controller of all; this is the cause of every other thing; this is the source of all origin and destruction  of all being too.
Mantra 5:  Naantah prajnyam na bahih prjnyam nobhayatah prajnyam naprjnyaghanam  naprjnyam naaprjnyam | adrishtam-vyavahaarya m-agraahyam-alakshanm-achintyam-vyapadesya-maikaamya-pratyamyasaaram  prapanchopasamam saantam sivamadvaitam chaturtham manyante sa aatmaa sa vijnyeyah ||
They consider the fourth state to be that which is not `consciousness of the internal world; nor consciousness of the external world (Taijasa); nor the consciousness of both the internal and external worlds. It is not Prajnyanaghana or mass of consciousness nor simple consciousness; nor unconsciousness, that is not visible external sense organs.
Avyahaaryam=  Not accessible to Karmendriyas; Agraahyam= not grasped by the mind; Alakshanam=not inferable; Achintyam avyapadesyam=Not possible of being thought as this is like this, and not possible of being described as such; Aikaatmya pratyaasaaram= It is the object of awareness that is one Prapanchopasamam—In which even the world of Sankarashana, Pradyumna, Aniruddha and others cease.  Advaitam=bereft of a second entity of a similar nature--this is known as Vasudeva. Sa aatmaa sa vijneyah= That is Aatman; That is to be known.
In this Mantra the fourth quarter Vasudeva is expounded. The Thureeya or the fourth state is different from Viswa, Taijasa and Prajnya states. The Vasudeva Murthy is  described as one who cannot be grasped.
He is the One without the second. He is Atman or the Universal Self. He should be known or realized. This is the super-conscious state. Here there is no outward or inward, it is beyond all intellect and senses. It is Lord alone who is   Infinite peace and Love, who should be realized and enjoyed in the last quarter.
The Consciousness in us is certainly the womb of all things, because if Consciousness were not in us neither the Sun, nor the moon, nor the stars, nor the entire world of objects nor the world of ideas would have been existent. When this   Conscious Principle is projected out through the mind and intellect and through the sense organs, then it expresses itself in the awareness of the world-objects and the world of ideas and thoughts.  If we remove this Principle of Awareness or Consciousness from a particular body, that body will no more illuminate for itself the ideas of this outside word. Thus scientifically, not philosophically spiritually, that the world outside and the world within, rise up from this Pure Consciousness, exist in this Consciousness and shall, when the Consciousness is withdrawn, merge back into Consciousness itself. Law of Consciousness follows Law of Matter.

It is beneficial here to go through the vivid and clear explanation of Sankaracharya on the three states described above.  Jagadguru Sankaracharya describes these three states in his Tattvabodha as follows:
The Waking State:
Jagradavastha kaa? srotraadri-jnyaanendriyaih sabdaadi-vishayaischa jnyaayate iti yaa  saa jaagradavasthaa | sthoolasareeraabhimaanee aatmaa viswa ityuchyate ||
What is waking state? That state of experience in which the sense objects like sound are perceived through sense organs like the ears, is the Waking State.  The Self identifying with the gross body, is called Viswa.
This is the State in which the entire personality turns outward, awake and fully functioning. The Self   identifies with all the three bodies (gross, subtle and causal) and experiences the world with them. The person in his wakeful state is called Viswa or complete or all-inclusive.
The Dream State:
Swapnaavasthaa keti chet jaaggrdaavasthaayaam yad drishtam  yat srutam tajjanita-vaasanayaa nidraasamaye yah | prapanchah prateeyate saa swapnaavasthaa | Sookshamsareera-abhimaaneeaatmaa taijasa ityuchyate ||
The explanation for dream State is as follows: The world that is visualized while in sleep from the impressions what was seen and heard in the waking state is called the Dreaming State. The Self here identifies with the subtle body and is called Taijasa.
Dreams are not fulfilled desires of the one who is in a wakeful state. One may dream of being a millionaire a or flying round the globe. Dreams are often illogical, ridiculous and often    silly to the man in wakeful state. The Self does not identify with the gross body in the dream state and it identifies only with the subtle and casual bodies. The individual is then called Taijasa as the dream world is thought-created. The dream may seem unreal to the one who is wakeful but it is real to the dreamer.
The Deep Sleep State
Atha sushupty-avasthaa kaa? Aham kimapi na jaanami |  Sukhena mayaa nidr-anubhooyata iti sushuptyavasthaa | karana sareer-abhimanee aatmaa prajnya ityuchyate ||
Then what is the Deep Sleep State?  That state about which ne says that “I did not know anything”  I slept like a log: I enjoyed a good sleep” is the Deep Sleep state. The Self identifies with the Causal body and is called Prajnya.
In the waking state we identify with the gross body and turn outwards and become the doer and   enjoyer. In the dream state we identify with our subtle body and become the enjoyer of the dream and fantasy or horror world; in the deep sleep state there is neither the doer nor the enjoyer of the world. There is no concept of time space or duality as in the other two states.   There is no cognizance in the deep sleep state. We are ignorant of our true nature therefore one who is in this state is called Prajnya (praayena Ajnyah) one who is more are less ignorant. In the wakeful and dream state each of us differs. In the Deep Sleep state we are all one and the same. The rich, the poor, the ignorant and the wise all experience the same bliss in the Deep Sleep state. In the eyes of god we are all the same in this state and are not influenced by individual factors.  The three states come and go. Each negates the experience and reality of the other two.  We stand as witness of these states, un-negated by them. The Self does   not take the   roles of the Wakeful, Dreamer or Deep Sleeper.
Mantra 1: Soyayamaatmaadhyaksharram-omkaaro adhi-maatram paadaa maatra maatraascha-paadaa  akaaara  ukaaroe makaara iti ||
This Self (Tureeya) exists in the Syllable OM. Tureeya corresponds to the syllable OM made up of three letters. Though indivisible it has the three sounds of Akaara, Ukaara and Makaara. 
OMkaara is a sound (naadaatmaka) and that itself is Atman.  The four quarters of Brahman  are expounded as Aniruddha, Pradyumna,   Sankarshana and Vasudeva corresponding to maatras A, U, M and ardha matra (half nasal  sound). The Upanishad is here vouchsafing to us that the three maatras (letters) are the three paadas.

Mantra 2-- Jaagaritasthaano Vaiswaanaro akaarah prathamaa maatra apter-aadimachvaadvaa aapnoti ha vai sarvaan kaamanaadischa  bhavati ya evam veda ||
Vaiswanara has the waking state as his sphere.  He is the first letter (A of AUM) of the pervasiveness or being the first. He who meditates thus attains all desirable things and becomes the foremost of all.
Akaara is the source of all speech and it provides all terms.  This is like Aniruddha who is all pervading.  Anirudddha is called Jagriti Sthaana and Vaiswanara.  Vaiswanara is to be known as having   “A” symbol as he is designated by the term akaara which is the source of all terms. Through mastery of senses one obtains the fruit of his desire and attains greatness.
The sound A (A -as in America) Is the very fundamental of sounds. Man has only to open his mouth, equipment of speech, and blow out some air to produce the initial sound A.     When a child is just born the very first sound it declares itself to the world is by crying A produced. The first letter ‘A’ seems to be in all languages of the world. All sounds are pervaded by A. Vaiswanara represented by A pervades the entire universe.
Mantra 3.   Swapnasthaanas-teijasa ukaaro dwiteeyaa maatrotkarshaad-ubhayatvaadvaa | utkarshati  ha vai jnaanasantatim samaanascha bhavati | naasya-brahmavitkule bhavati ya evam veda ||
He who is Taijasa having the dream state as his field of activity denotes the second letter U (ukaara) because of the similarity of the excellence with Prajnya. He who thus meditates on Taijasa or Pradyumna will become celebrated on account of the spreading of knowledge among disciples and their disciples and become equal to all great persons. Nobody will be born in his lineage who is not a knower of Brahman.
Through mastering the dreams the spiritual seeker reaches the peak of wisdom by meditating on the second letter as Pradyumna. Everyone in their family will be knowers of Brhaman or spiritual seekers like him.
The letter U comes after A in AUM And hence the superior   of dream state over wakeful state. The letter U comes in between in AUM. Dream state comes in between waking and the deep sleep state.  He who meditates upon U sound in AUM and the subtle body or pradyumna develops his  mind to such an extraordinary perfection that he certainly attains a superior knowledge and he should prove himself in the world great genius. 
Following the psychological heredity in the family noticed in humanity Upanishad says that in the family of such learned and erudite scholars of the scriptures, there will not be any member who is culturally low and spiritually wanting.
Mantra 4 Sushuptasthaanah  praajnyo makaaras-triteeyaa maatra | miterapeetervaa | minotee ha vaa ida(ga)m sarvam-apeetascha bhavati  ya evam veda ||
Praajnya with his sphere of activity in the   Deep Sleep state is the third letter “Ma” because of measuring or because of absorbing everything. He who knows thus measure as all this and becomes the place of absorption or gets merged in all.
By a mind of tranquility they find their stature and inspire all others around to grow. In Makaara   Akaaraa and Ukaara merge. With Akaara you start    a sound, with Ukaara you continue and with Makaara  you close the sound hence the merger in Ma. In the Prajnya or Sankarsha the world merges. The spiritual seeker merges in Paramaatman and thereafter he is called apeetascha bhavati (place of absorption). Apeeta means pralaya or cataclysm.
In pronouncing the sound AUM the letters A and U merge themselves into the last sound M. When we chant the sound AUM, A and U seem to rise up.  In the deep sleep state of Consciousness, both the waking state and the dream state experiences seem to fold themselves into a mass of homogeneous awareness. On waking up out of this undifferentiated mass of Consciousness the deep sleep state the waking and the dream states seem to emerge out.
 One other common feature between the last letter in AUM and the deep sleep state is the obvious fact that in both the earlier plurality of differences merge themselves to become one whole.

LAST MANTRA: Amaatraschaturthoavyavahaaryah prapanchopasamah sivo advaita evam-omkaara aatmaiva samvisatyaatmanaa-aatmanam  ya evam veda ||
The fourth stage which is bereft of all limitations, is the Supreme state of Atman alone (Vyuha Vasudeva eva)  and is of the form of OMkaara. Atman is not visible to the Indriyas. The world of Aniruddha, Pradyumna and Sankarshana are absorbed in it. It is one without any second entity (adviatam). It is the auspicious one (sivam). This is the sound of AUM. He who knows thus attains Paramaaatman by the grace of Paramaatman alone.
The fourth Tureeya is beyond all the three syllables. It is in it the whole world dissolves. It is Aatman the Self. It is beyond birth and death everlasting peace of joy. In Vaishnava Theology the fourth state is addressed as Paravasudeva. There is very little difference between Vasudeva and Paravasudeva. In fact there are two opinions as to Vyuhas. Some think it is three and others four. Naantah prajnyam in   one of the verses refer to Paravasudeva.
Viswa, Tejasa and Prajnya are super-impositions upon the Supreme Reality, which is the fourth state, Tureeya—Eternal, Immortal, Knowledge, Absolute, and in essence nothing but ‘Bliss’. He who knows this merges his Self in the Supreme Self—the individual in the Total.
In these 12 mantras above the characteristics of four Vyuhas and the particular states to which they relate are described.  The Supreme Reality into which we merge in the “fourth state” (Tureeya) is also represented by the sacred syllable AUM. In our Sandhyavandana mantra we meditate on “Bhurbhuvassuvarom” meaning the three worlds Bhoo, Bhuvah and Suvah are AUM alone are Brhamaatmaka representing Brahman. MNU also says AUM tad Brahma tad Aatma— AUM is Brahman and that is Aatma.  AUM is our innermost sacred voice that we try to explore and understand all our life seeking liberation.
The sage in Mandookya Upanishad says the three worlds or orders of Reality are visualized in the sounds of the sacred syllable—a, u, and m—as it is manifested in the phenomenon world as Saguna Brahman. All Veda Mantras according to Mandooka go back to AUM, and then beyond even this primordial energy to Nirguna Brahma--the ultimate goal of all spiritual seekers. He also says how it is beneficial to meditate upon these four aspects as Paramaatman, Supreme Being and derive great benefits to get Saayujya or be one with Brahman.
In Muktika Upanishad there is a brief reference but most glorious review on Mandookya Upanishad as follows: “Mandookyam ekam kevalam mumkshatvam vimukta ye”—Mandookya Upanishad alone is sufficient for an aspirant to attain liberation.
Mandookya Upanishad containing only 12 mantras, because of it brevity it, makes difficult for the Vedanta students to understand its entire import without elaborate explanation. Therefore, Garudapada the Guru of Sankara has written a Karika (Gloss) upon this Upanishad.  Karikas are memorial verses written with a view to expounding in a metrical form an aspect of a subject or particular doctrine, so that it may be easily memorized by the student. His entire text of this Karika falls under four chapters. The Karika contains 215 verses in four chapters; Agama Prakarana (scriptural text portion); Vaithathya Prakarana (Illusory portion); Advaita Prakarana (Non-dualism philosophy) and Alatha Santhi Prakarana (Quenching the Firebrand). You can thus see how this great Upanishad has attracted the attention of great Gurus like Sankara, Madhva and others from the very early times. In this sense my attempt in this compilation from great authors is a trivial attempt but its rendering in English may inspire many to go through this Upanishad more in detail.
1.      Ananta Rangacharya N.S., Principal Upanishads, Mandookyopanishat, Bengaluru, India.
2.      Swami Harshananda, The Ten cardinal Upanishads, Ramakrishna Math, Chennai, India.
3.      Eknath Easwaran, The Upanishads, Nilgiri Press,
4.      Swami Tejomayananda, Tattva- Bodha, Central Chinmaya Mission Trust, Mumbai, India
5.      Ramachandra Rao S.K.,  Darsanodaya, Kalpatharu Research Academy, Sarada Peetham, Bengaluru, India
6.      Swami Chinmayananda,  Mandookya Upanishad, Central Chinmaya Mission Trust, Mumbai, India
7.      Ananta Rangacharya, Vedanta Sutras, Bengaluru, India.
8.       Swami Viditananda, Bhaja Govindam, Adhyatma  Vidya Mandir, Ahmadebad, India.

Commentary on Mandukya Upanishad

AUM is All Harih Aum!

AUM, the word, is all this, the whole universe. A clear explanation of it is as follows: All that is past, present and future is, indeed, AUM. And whatever else there is, beyond the threefold division of time—that also is truly AUM. (1.1)

All This is Brahman All this is, indeed, Brahman. This Atman is Brahman. This same Atman has four quarters. (1.2)

[The first three quarters correspond to the letters of AUM: 1 = A, 2 = U, 3 = M. The fourth quarter is silence.]

 "A" — Waking State The first quarter is called Vaisvanara, whose sphere of activity is the waking state, who is conscious of external objects, who has seven limbs and nineteen mouths and who is the experienced of gross objects. (1.3)

"U" — Dream State The second quarter is Taijasa, whose sphere of activity is the dream state, who is conscious of internal objects, who is endowed with seven limbs and nineteen mouths and who is the experienced of subtle objects. (1.4)

"M" — Deep Sleep that is the state of deep sleep wherein one asleep neither desires any object nor sees any dream. The third quarter is Prajna, whose sphere is deep sleep, in whom all experiences become unified, who is, verily, a mass of consciousness, who is full of bliss and experiences bliss and who is the door leading to the knowledge of dreaming and waking. (1.5)

He is the Lord of all. He is the knower of all. He is the inner controller. He is the source of all; for from him all beings originate and in him they finally disappear. (1.6)

Gaudapada Karika Explanation (Ch 1)

[Gaudapada (c. 8th century CE) was first philosopher of the Advaita Vedanta school of Hindu philosophy in the post-Upanishadic period. He was guru of the great teacher Adi Shankara.]

Visva is all—pervading, the experienced of external objects. Taijasa is the cognizer of internal objects. Prajna is a mass of consciousness. It is one alone that is thus known in the three states. Visva is the cognizer through the right eye; Taijasa is the cognizer through the mind within; Prajna is the akasa in the heart. Therefore the one Atman is perceived threefold in the same body. Visva experiences the gross; Taijasa, the subtle; and Prajna, the blissful. Know these to be the threefold experience. The gross object satisfies Visva; the subtle, Taijasa; and the blissful, Prajna. Know these to be the threefold satisfaction. The experienced and the objects of experience associated with the three states have been described. He who knows these both does not become attached to objects though enjoying them. Surely a coming into existence must be predicated of all positive entities that exist. Prana manifests all inanimate objects. The Purusha manifests the conscious beings in their manifold forms. Some of those who contemplate the process of creation regard it as the manifestation of God’s powers; others imagine creation to be like dreams and illusions. Those who are convinced about the reality of manifested objects ascribe the manifestation solely to God’s will, while those who speculate about time regard time as the creator of things. Some say that the manifestation is or the purpose of God’s enjoyment, while others attribute it to His division. But it is the very nature of the effulgent Being. What desire is possible for Him who is the fulfillment of all desires?

Turiya 'the fourth' — Pure Consciousness Turiya is not that which is conscious of the inner (subjective) world, nor that which is conscious of the outer (objective) world, nor that which is conscious of both, nor that which is a mass of consciousness. It is not simple consciousness nor is It unconsciousness. It is unperceived, unrelated, incomprehensible, un-inferable, unthinkable and indescribable. The essence of the Consciousness manifesting as the self in the three states, It is the cessation of all phenomena; It is all peace, all bliss and non-dual. This is what is known as the Fourth (Turiya). This is Atman and this has to be realized. (1.7)

Gaudapada Karika Explanation

Turiya, the changeless Ruler, is capable of destroying all miseries. All other entities being unreal, the non-dual Turiya alone is known as effulgent and all—pervading. Visva and Taijasa are conditioned by cause and effect. Prajna is conditioned by cause alone. Neither cause nor effect exists in Turiya. Prajna does not know anything of self or non-self, of truth or untruth. But Turiya is ever existent and all—seeing. Non-cognition of duality is common to both Prajna and Turiya. But Prajna is associated with sleep in the form of cause and this sleep does not exist in Turiya. The first two, Visva and Taijasa, are associated with dreaming and sleep respectively; Prajna, with Sleep bereft of dreams. Knowers of Brahman see neither sleep nor dreams in Turiya. Dreaming is the wrong cognition and sleep the non-cognition, of Reality. When the erroneous knowledge in these two is destroyed, Turiya is realized. When the Jiva, asleep under the influence of beginning-less maya, is awakened, it then realizes birthless, sleepless and dreamless Non-duality. If the phenomenal universe were real, then certainly it would disappear. The universe of duality which is cognized is mere illusion (maya); Non-duality alone is the Supreme Reality. If anyone imagines illusory ideas such as the teacher, the taught and the scriptures, then they will disappear. These ideas are for the purpose of instruction. Duality ceases to exist when Reality is known. (GK1.10-18)

A + U + M Aum explained.

The same Atman explained before as being endowed with four quarters is now described from the standpoint of the syllable AUM. AUM, too, divided into parts, is viewed from the standpoint of letters. The quarters of Atman are the same as the letters of AUM and the letters are the same as the quarters. The letters are A, U and M. (1.8)

Vaisvanara Atman, whose sphere of activity is the waking state, is A, the first letter of AUM, on account of his all— pervasiveness or on account of his being the first. He who knows this obtains all desires and becomes first among the great. (1.9)

 Taijasa Atman, whose sphere of activity is the dream state, is U, the second letter of AUM, on account of his superiority or intermediateness. He who knows this attains a superior knowledge, receives equal treatment from all and finds in his family no one ignorant of Brahman. (1.10)

Prajna Atman, whose sphere is deep sleep, is M, the third letter of AUM, because both are the measure and also because in them all become one. He who knows this is able to measure all and also comprehends all within himself. (1.11)

The Fourth (Turiya) is without parts and without relationship; It is the cessation of phenomena; It is all good and non-dual. This AUM is verily Atman. He who knows this merges his self in Atman—yea, he who knows this. (1.12)

Commentary by Shankaracharya

Those who have realized Brahman, the Highest Reality, merge the self in Turiya because they have transcended the notion of cause and effect, which inheres in the third quarter of Atman. They are not born again; for they have realized their identity with the causeless Turiya. The illusory snake which has merged in the rope as a result of discrimination between the snake and the rope, does not reappear. Students of dull or mediocre mind who have renounced the world and are endowed with spiritual virtues should meditate on the common features of the sounds of AUM and the quarters of Atman, as explained before. Thus, proceeding step by step, they ultimately realize Turiya, devoid of any state or sound, and attain the Highest Goal. Gaudapada Karika Explanation AUM should be known quarter by quarter. There is no doubt that the quarters are the same as the letters. Having understood AUM quarter by quarter, one should not think of anything else. The mind should be concentrated on Aum. Aum is the fearless Brahman. He who is always absorbed in Aum knows no fear whatever. Aum is verily the Lower Brahman. It is also stated to be the Higher Brahman. Aum is beginning-less and unique. There is nothing outside it. It is unrelated to any effect and is immutable. Aum is, indeed, the beginning, middle, and end of all things. He who has realized Aum as immutable immediately attains the Supreme Reality. Know Aum to be Isvara, ever present in the hearts of all. The calm soul, contemplating Aum as all-pervading, does not grieve. One who knows Aum, which is soundless and also endowed with infinite sounds, which is all good and the negation of duality, is a real sage, and none other. (GK 1.24-29)
--Excerpts translated by Swami Nikhilananda