Krishna establishes a lineage for what he is about to teach. This knowledge is not new, he says. Sages have sung it in many ways. Different Vedic hymns have expressed it. And the Brahma Sutras — those carefully reasoned aphorisms — have established it conclusively.
There is comfort in this. Like a grandmother saying, 'This is not something I just made up. Our elders said the same thing. It has been tested across generations.' Krishna reassures Arjuna that the teaching ahead rests on ancient, well-examined ground.