Verse 17.23
ॐतत्सदिति निर्देशो ब्रह्मणस्त्रिविधः स्मृतः । ब्राह्मणास्तेन वेदाश्च यज्ञाश्च विहिताः पुरा ॥ १७.२३ ...
ओउम्, तत्, सत् —- ऐसे यह तीन प्रकार का सच्चिदानन्दधन ब्रह्म का नाम कहा है ; उसी से सृष्टि के आदि काल में ब्राह्मण और वेद तथा यज्ञादि रचे गये |
AUM, TAT, SAT (literal translation: the Lord who is the truth). Dear Partha, each one of these sacred words represents the three stages of the Brahman (the Brahman is the single word that describes where all Brahmins (spiritual teachers) have originated from). From the Brahman also evolved the Holy Scriptures (Vedas) and is today also known as the Supreme Spiritual Sacrifice.