OM or AUM is of paramount importance in Hinduism.this symbol is a sacred syllable representing Brahman.Brahman itself is incomprehensible , so a symbol becomes mandatory to help us realize the unknowable. OM represents both the unmanifest(nirguna) and manifest(saguna) aspects of God.That is why it is called Pranava, to mean that it pervades life and runs through our prana or breath.
OM is placed at the beginning and end of a reading of the Vedas or prior to any prayer.
According to Monier Williams”OM is the mystic name for the Hindu Triad, and represents the union of the three Gods,viz.,a(Vishnu), u(Shiva), m*brahma);Buddhists place Om at the beginning of their vidya Shadakshari viz.,(om man padma hum). According to our ancient textsOm may be used in the following senses: Pranava, arambhe, svikare, asvikare, mangale, shubhe,jneye, Brahmani.
With preceding a or a a, the o of OM does not form vriddhi(au), but forms guna(o). (Pan 6.1.95)”
OM appears first in the Upanishads as a mystic monosyllable and is there setforth as the object of profound religious meditation, the highest spiritual efficacy being attributed not only to the whole word but also to the three sounds a,u,m.
Mandukya Upanishad: The Mandukya Upanishad deals with the symbolic significance of the sacred syllable OM and its correlation with the four states of consciousness namely the wakeful consciousness, dream state, the state of deep sleep or dreamless sleep and the state of transcendental consciousness in which all divisions and duality disappears and the self alone exists in the pure state, all by itself.
In the first sloka it says”:Om iti etadekasharam idam sarvam”
“This syllable OMis verily all this
This is the explanation about OM
The past, the present and the future are OM
And that beyond these there is OM.”
Taittiriya Upanishad: In its first chapter describes OM as Brahman(Om iti Brahma , OM iti sarvam)
Saivya Satyakama asked pippalada: 'Sir, if some one among men should meditate here until death on the syllable Om, what would he obtain by it?'
2. He replied: 'O Satyakama, the syllable Om (AUM) is the highest and also the other Brahman; therefore he who knows it arrives by the same means at one of the two.
3. If he meditate on one Matra (the A), then, being enlightened by that only, he arrives quickly at the earth. The Rik-verses lead him to the world of men, and being endowed there with penance, abstinence, and faith, he enjoys greatness.
4. If he meditate with two Matras (A + U) he arrives at the Manas 5, and is led up by the Yagusverses to the sky, to the Soma-world. Having enjoyed greatness in the Soma-world, he returns again.
5. Again, he who meditates with this syllable AUM of three matras, on the Highest Person, he comes to light and to the sun. And as a snake is freed from its skin, so is he freed from evil. He is led up by the Saman-verses to the Brahma-world; and from him, full of life (Hiranyagarbha, the lord of the Satya-loka), he learns to see the all-pervading, the Highest Person.
The Chandogya Upanishad is one of the oldest Upanishads of Hinduism. It opens with the recommendation that "let a man meditate on Om". It calls the syllable Om as udgitha (उद्गीथ, song, chant), and asserts that the significance of the syllable is thus:
The essence of all these beings is the earth. The essence of the earth is water. The essence of water is vegetation. The essence of vegetation is man. The essence of man is speech. The essence of speech is Rik. The essence of Rik is Saman. The essence of Saman is Udgitha. The syllable Om which is called Udgitha, is the quintessence of the essences, the supreme.
Rik (ऋच्, Ṛc) is speech, states the text, and Sāman (सामन्) is breath; they are pairs, and because they have love and desire for each other, speech and breath find themselves together and mate to produce song. The highest song is Om, asserts section 1.1 of Chandogya Upanishad. It is the symbol of awe, of reverence, of threefold knowledge because Adhvaryu invokes it, the Hotr recites it, and Udgatr sings it.
The second volume of the first chapter continues its discussion of syllable Om, explaining its use as a struggle between Devas (gods) and Asuras (demons). Max Muller states that this struggle between gods and demons is considered allegorical by ancient Indian scholars, as good and evil inclinations within man, respectively.The legend in section 1.2 of Chandogya Upanishad states that gods took the Udgitha (song of Om) unto themselves, thinking, "with this [song] we shall overcome the demons"The syllable Om is thus implied as that which inspires the good inclinations within each person.
Chandogya Upanishad's exposition of syllable Om in its opening chapter combines etymological speculations, symbolism, metric structure and philosophical themes.eaning and significance of Om evolves into a philosophical discourse, such as in section 2.10 where Om is linked to the Highest Selfand section 2.23 where the text asserts Om is the essence of three forms of knowledge, Om is Brahman and "Om is all this. “
Katha Upanishad:The Katha Upanishad is the legendary story of a little boy, Nachiketa – the son of sage Vajasravasa, who meets Yama – the Indian deity of death. Their conversation evolves to a discussion of the nature of man, knowledge, Atman (Soul, Self) and moksha (liberation) In section 1.2, Katha Upanishad characterizes Knowledge/Wisdom as the pursuit of good, and Ignorance/Delusion as the pursuit of pleasant, that the essence of Veda is to make man liberated and free, look past what has happened and what has not happened, free from the past and the future, beyond good and evil, and one word for this essence is the word Om.
The word which all the Vedas proclaim,
That which is expressed in every Tapas (penance, austerity, meditation),
That for which they live the life of a Brahmacharin,
Understand that word in its essence: Om! that is the word.
Yes, this syllable is Brahman,
This syllable is the highest.
He who knows that syllable,
Whatever he desires, is his.
— Katha Upanishad, 1.2.15-1.2.16
The Maitrayaniya Upanishad in sixth Prapathakas (lesson) discusses the meaning and significance of Om. The text asserts that Om represents Brahman-Atman. The three roots of the syllable, states the Maitri Upanishad, are A + U + M.[ The sound is the body of Soul, and it repeatedly manifests in three: as gender-endowed body - feminine, masculine, neuter; as light-endowed body - Agni, Vayu and Aditya; as deity-endowed body - Brahma, Rudra and Vishnu; as mouth-endowed body - Garhapatya, Dakshinagni and Ahavaniya; as knowledge-endowed body - Rig, Saman and Yajur; as world-endowed body - Bhūr, Bhuvaḥ and Svaḥ; as time-endowed body - Past, Present and Future; as heat-endowed body - Breath, Fire and Sun; as growth-endowed body - Food, Water and Moon; as thought-endowed body - intellect, mind and pysche. Brahman exists in two forms - the material form, and the immaterial formless The material form is changing, unreal. The immaterial formless isn't changing, real. The immortal formless is truth, the truth is the Brahman, the Brahman is the light, the light is the Sun which is the syllable Om as the Self. The world is Om, its light is Sun, and the Sun is also the light of the syllable Om, asserts the Upanishad. Meditating on Om, is acknowledging and meditating on the Brahman-Atman (Soul, Self)
The Mundaka Upanishad in the second Mundakam (part), suggests the means to knowing the Self and the Brahman to be meditation, self-reflection and introspection, that can be aided by the symbol Om.
That which is flaming, which is subtler than the subtle,
on which the worlds are set, and their inhabitants –
That is the indestructible Brahman. It is life, it is speech, it is mind. That is the real. It is immortal.
It is a mark to be penetrated. Penetrate It, my friend.
Taking as a bow the great weapon of the Upanishad,
one should put upon it an arrow sharpened by meditation,
Stretching it with a thought directed to the essence of That,
Penetrate that Imperishable as the mark, my friend.
Om is the bow, the arrow is the Soul, Brahman the mark,
By the undistracted man is It to be penetrated,
One should come to be in It,
as the arrow becomes one with the mark.
— Mundaka Upanishad, 2.2.2 - 2.2.4
Adi Shankara, in his review of the Mundaka Upanishad, states Om as a symbolism for Atman (soul, self). The Mandukya Upanishad opens by declaring, "Om!, this syllable is this whole world". Thereafter it presents various explanations and theories on what it means and signifies. This discussion is built on a structure of "four fourths" or "fourfold", derived from A + U + M + "silence" (or without an element).
Aum as all states of time
In verse 1, the Upanishad states that time is threefold: the past, the present and the future, that these three are "Aum". The four fourth of time is that which transcends time, that too is "Aum" expressed.
Aum as all states of Atman
In verse 2, states the Upanishad, everything is Brahman, but Brahman is Atman (the Soul, Self), and that the Atman is fourfold. Johnston summarizes these four states of Self, respectively, as seeking the physical, seeking inner thought, seeking the causes and spiritual consciousness, and the fourth state is realizing oneness with the Self, the Eternal.
Aum as all states of consciousness
In verses 3 to 6, the Mandukya Upanishad enumerates four states of consciousness: wakeful, dream, deep sleep and the state of ekatma (being one with Self, the oneness of Self). These four are A + U + M + "without an element" respectively.
Aum as all of knowledge
In verses 9 to 12, the Mandukya Upanishad enumerates fourfold etymological roots of the syllable "Aum". It states that the first element of "Aum" is A, which is from Apti (obtaining, reaching) or from Adimatva (being first). The second element is U, which is from Utkarsa (exaltation) or from Ubhayatva (intermediateness). The third element is M, from Miti (erecting, constructing) or from Mi Minati, or apīti (annihilation) The fourth is without an element, without development, beyond the expanse of universe. In this way, states the Upanishad, the syllable Om is indeed the Atman (the self).
The Shvetashvatara Upanishad, in verses 1.14 to 1.16, suggests meditating with the help of syllable Om, where one's perishable body is like one fuel-stick and the syllable Om is the second fuel-stick, which with discipline and diligent rubbing of the sticks unleashes the concealed fire of thought and awareness within. Such knowledge, asserts the Upanishad, is the goal of Upanishads. The text asserts that Om is a tool of meditation empowering one to know the God within oneself, to realize one's Atman (Soul, Self).
It is the syllable which preceded the universe and from which the gods were created. It is the "root" syllable (mula mantra), the cosmic vibration that holds together the atoms of the world and heavens. Indeed the Upanishads say that AUM is god in the form of sound. Thus OM is the first part of the most important mantras in both Buddhism and Hinduism, e.g. Om Namoh Shivai and Om Mani Padme Hum.