Bhagavad Gita, Chapter 17, Verse 23

'Om, Tat, Sat': this has been declared to be the triple designation of Brahman. By that were made of old the Brâhmanas, the Vedas and the Yajnas.

Three real, specific words are named here as carrying the weight of the Absolute Truth itself.

Krishna doesn't leave this truth entirely abstract, he ties it to concrete, sacred syllables that can actually be spoken. Real language is given to something otherwise beyond words.