The word is also linked to the sound of breath and a subtle and high potency universal vibration which can be heard internally in the subtle planes as a deep sound (pranava nada) by the adepts all the time. It is possible that the word might have been integrated into Vedic religion from some ascetic tradition of ancient India.
The Chandogya Upanishad narrates how the syllable Aum issued forth from Brahma as he brooded upon the worlds he created in the initial stages of creation. From his brooding first emerged the threefold knowledge (trayi vidya) and then the syllables bhur, bhuvah and suvah. When he brooded upon them (bhur, bhuvah and suvah), the syllable Aum issued forth from them. Thus symbolically, Aum represents the entire creation manifested in the three planes, namely the earth, the mid region and the heaven.
The word Om is not mentioned directly in the earliest hymns of the Rigveda, but it is mentioned in the other Vedas and several Upanishads associated with them. Initially, in the early Vedic period, because of the sanctity associated with it, the word was kept as a secret and never uttered in public. It was used in private conversations and passed on from teacher to disciple or father to son directly and in secrecy.
It was also not used in the rituals. Because it was not permitted to use the word directly, some early Upanishads referred to it indirectly as the udgita (upsound) or pranava (calling out), alluding to its significance in regulated breathing and religious chanting respectively.
Other expressions used in the scriptures in reference to it are vācaka (symbol), tārāka (crossing) and akshara (imperishable word). It is also described as Brāhman in sound form (Sabda Brāhman). In the Bhagavadgita Lord Krishna declares that of the utterances He is the monosyllable Aum.
OM Pranava and Udgita
In the Vedic scriptures, the word is mentioned for the first time openly in the first hymn of the Shukla (white) Yajurveda. Some believe this may be a later day interjection, since in the Taittiriya Samhita (5.2.8) of the White Yajurveda, it is sill mentioned indirectly as a divine quality (deva lakshna) having three modes of expression (tri-alikhita), an expression that is commonly associated with Aum.We find increasing references to it in many Upanishads that were composed in the Post Rigvedic period such as Brihadaranyaka, Chandogya, Taittiriya and Mandukya Upanishads. These Upanishads draw its symbolic significance by associating it with the Universal Self or Supreme Brāhman. They directly refer to it as Om, Aum, Udgita, Pranava and Omkara. In some verses of the Brihadaranyaka Upanishad, Om is used as an affirmation in the sense of "Yes I agree."
The Chandogya Upanishad informs the various ways in which udgita can be meditated and the benefits arising from them. It declares that by meditating upon it one can dispel darkness and fear, gain strength, become rich in food and gain immortality. In some verses it equates Aum with the space (akasa).
Patanjali's Yogasutra states that Isvara (the Self) is expressed as Pranava . Its continuous chanting (japa) would lead to the mastery of the right knowledge and removal of interruptions (antarayas) which arise in the form of distractions (vikshepas) such as disease and dullness.
Yoga tradition holds that chanting of the word continuously would bring many benefits, such as purification of the mind, the body and the environment, removal of the sins, equanimity of the mind, removal of desires, delusion and attachment and attainment of all the four aims of human life, namely obligatory duty(dharma), wealth (artha), pleasure (kama) and liberation (moksha).
Aum and Om in the Upanishads
Both the major and minor Upanishads repeatedly mention the symbolic and spiritual significance of Aum or Om and recommend meditation upon it as the means to achieve the state of Brāhman. Descriptions of aum in various major and minor Upanishads are mentioned below.
In the Vedic literature we find a gradual evolution of Aum from Om. The word aum was used for the first time in the Mandukya Upanishad to explain Brāhman as the only and the ultimate reality, a concept that became the basis subsequently for the emergence of Advaita Vedanta or the philosophy of monism. Gaudapada expounded this philosophy through his commentary on the Upanishads whcih is known as Mandukya Karika.
In its very opening verse, the Mandukya Upanishad describes the significance of Aum in which it declares Omkara as everything (idam sarvam), the past, the present and the future and also whatever there is beyond the threefold time. As the ultimate Brāhman it has four quarters, the waking state (jagrata) presided by Vaisvanara (universal man), the dream state (svapna) presided by taijasa (illumined being), deep sleep state (susupta) presided by prajna (intelligent being) and the transcendental state (turiya) presided by the individual Self (atman) which in reality is but Brāhman Himself.
We can see these four states being represented in the syllable AUM. The waking state is represented by the first letter A, the dream state by the second letter U, the deep sleep state by the third letter M and the fourth state (Self) by the syllable AUM itself. Like Patanjali, Gaudapada equates Aum with Isvara and suggests that by worshipping Him as Aum we will transcend suffering.
The fourfold nature of Aum is also represented truthfully in the symbol of Aum, which consists of four curves and one circle. The four curves represent the four states of consciousness and the circle represent the Self. The lower curve represents the waking state, the middle curve the dream state, the upper curve the deep sleep state, the semi circle detached from these three represent the transcendental state while the circle above all is the witnessing Self or the Supreme Self. Symbolism of Aum is depicted in the diagram above.
