Bhagavad Gita Chapter 17 Verse 23
भगवद् गीता अध्याय 17 श्लोक 23

तत्सदिति निर्देशो ब्रह्मणस्त्रिविधः स्मृतः।
ब्राह्मणास्तेन वेदाश्च यज्ञाश्च विहिताः पुरा।।17.23।।



हिंदी अनुवाद - स्वामी तेजोमयानंद
।।17.23।। ? तत् सत् ऐसा यह ब्रह्म का त्रिविध निर्देश (नाम) कहा गया है उसी से आदिकाल में (पुरा) ब्राहम्ण? वेद और यज्ञ निर्मित हुए हैं।।


Brahma Vaishnava Sampradaya - Commentary

Once again  the  Supreme  Lord  Krishna  discourses  on  the  modalities  of
performance of prescribed duties and the activities that are required to  be
performed by mentioning OM TAT SAT which  is  veritably  the  transcendental
sound vibration and names of the Supreme Lord in His abstract form.  In  all
creation His transcendental sound vibration OM is the  root  of  all  sounds
and all pervasively always vibrating  within  and  without.  Since  all  the
Vedic scriptures  refer  to  the  Supreme  Lord  with  such  veneration  and
reverence He is TAT and because the Supreme  Lord  is  perfect  without  any
defect and always auspicious He is SAT. In the  subsidiary  chapter  of  the
Rig Veda the word OM is referred to His potency of the brahman which is  the
spiritual substratum pervading all existence. TAT refers to Himself  as  the
source of the Brahman and SAT denotes that He is  the  original  creator  of
all existence. The elevated Vaisnavas and Brahmins  from  one  of  the  four
sampradayas or authorised channel of disciplic succession  as  revealed  in
Vedic  scriptures  are  ordained  to  vibrate  these  transcendental   sound
vibrations when commencing, executing and concluding all Vedic rites.