। ॥ २१ ॥
In plain words
The Veda's own sentences—tat tvam asi, 'That you are,' and others like it—therefore stand as a means of valid knowledge concerning Brahman. We now set out in full the reasoning by which they do so.
Close to the Sanskrit
Hence indeed the Vedic sentence beginning with 'That you are' stands as the means of valid knowledge concerning Brahman; and that reasoning by which it does so is fully proclaimed by us.