Translation
"Om, the sacred syllable, the supreme combination of letters" — the sound form of the Absolute Truth (Bhagavad-gita 8.13).
Meaning
The pranava "om" is the primordial sound of the Vedas. In Bhagavad-gita (8.13) Krishna says that one who leaves the body vibrating om and remembering Him attains the supreme goal. Srila Prabhupada explains that om, Brahman and Krishna are non-different; om is the impersonal sound representation of Krishna, also contained in the Hare Krishna mantra.
