The Mandukya Upanishad, belonging to the Atharvaveda, is the shortest yet most profound of the principal Upanishads. It consists of only twelve verses, but its depth is immense, as it systematically expounds the nature of the ultimate reality (Brahman) through the sacred syllable Om (AUM). The Upanishad identifies the four states of consciousness—waking (jagarita), dreaming (svapna), deep sleep (sushupti), and the fourth state (turiya)—with the three constituent phonemes of Om: A, U, M, and the silence that follows.
According to the Mandukya Upanishad 1.1, "Om ity etad aksharam idam sarvam" (Om, this syllable, is all this). The waking state corresponds to the phoneme 'A', the dreaming state to 'U', the deep sleep state to 'M', and turiya is the soundless, transcendent aspect beyond the three phonemes. The Gaudapada Karika, a seminal commentary on the Mandukya Upanishad, elaborates on the non-dual nature of turiya as the realization of the self (Atman) as identical with Brahman.
The mantra is traditionally chanted for self-realization and liberation (moksha), as it leads the practitioner to understand the illusory nature of the three ordinary states and to abide in the fourth, which is pure consciousness. The recommended chanting context is during meditation, preferably at dawn or dusk, with a count of 108 repetitions using a rudraksha mala. There are no specific cautions, but the mantra is considered powerful and should be chanted with proper understanding and reverence.
The Mandukya Upanishad itself states (verse 12) that one who knows this attains the supreme goal. The mantra is also associated with the deity Atman/Brahman, as it directly points to the non-dual self.
Om, this syllable is all this.
The mantra is built around the seed-syllable Oṁ, which itself comprises the three phonemes A, U, M, representing the three states of consciousness, and the silence after, representing turīya.