आद्यं यत्त्र्यक्षरं ब्रह्म त्रयी यस्मिन्प्रतिष्ठिता ।एकाक्षरं परं ब्रह्म प्राणायामः परं तपः ॥
In plain words
That first sound, three syllables long, is Brahman, and the whole threefold Veda rests inside it. One syllable — and it is the supreme Brahman. Holding the breath is the highest austerity there is.
Close to the Sanskrit
That primal Brahman which is of three syllables, in which the threefold Veda stands established — the one-syllabled supreme Brahman; restraint of the breath is the highest austerity.