Om is the most important MANTRA in Hinduism. CHANDOGYA UPANISHAD discusses the significance of om. There it is given the highest value, equiva-lent to the RIG VEDA and SAMA VEDA combined; it is said to be speech and breath combined. Om is also said to be the Sama Vedic chant encapsulated.
In TAITTIRIYA UPANISHAD 1.8 om is variously said to be BRAHMAN or the entire world. The MAN-DUKYA UPANISHAD outlines the esoteric aspects of om. It is said to be all that is—past, present, and future—and to transcend time. Om is said to be the Self (ATMAN). Esoterically, it is said to encom-pass the four STATES OF CONSCIOUSNESS: the waking, dreaming, deep-sleep, and transcendent states. For this purpose, using SANSKRIT grammar, the let-ter o in the word om is understood to constitute an a and a u. A is the waking state, u the dreaming state, m the deep-sleep state; the fourth state has no external marker and is the non-dual reality.
Later texts understand om to encompass all visible and invisible worlds, and these are enu-merated. It is seen to be the three gods: BRAHMA, VISHNU, and SHIVA; it is seen to be this world, the sky world, and the world of heaven; its letters are seen to be the manifest and unmanifest world; and so on. One of the most common MANTRAS using om is om tat sat: “om is that reality: all that exists.”
For a YOGI, to focus on the mantra om is to focus on the ultimate reality. If the yogi pro-nounces om, it reaches the crown CHAKRA; if the O
Om, the most revered syllable and mantra in San-skrit, is believed to encompass all visible and invisible worlds. (www.shutterstock.com/Junji Takemoto) yogi becomes absorbed meditationally in om, he becomes eternal. Om, too, is understood as the essence of the word brahman (shabda brahman) and is therefore, via its transcendent sound, the source of all manifest reality, where reality is known to be nothing but the congealing of sound. No mantra begins without om and most Vedic mantras end with om as well. Om is often referred to as Omkara (the kara, a meaningless marker), added to make it easier to distinguish visually in Sanskrit script. It is also called pranava, which literally means, “That which resounds.”
Further reading: Cornelia Dimitt and J. A. van Buite-nen, eds. and trans., Classical Hindu Mythology: A Reader in the Sanskrit Puranas (Philadelphia: Temple University Press, 1978); S. Ranganath, Aum-Pranava in Indian Tradition (Delhi: Eastern Book Linkers, 2001).
Encyclopedia of Hinduism. A. Jones and James D. Ryan. 2007.