That which is brilliant, smaller than small, that on which the worlds are founded and their inhabitants, that is the indestructible Brahman, that is the breath, speech, mind; that is the true, that is the immortal. That is to be hit. Hit it, O friend!

In plain words: Brahman, the ultimate reality, is shining and smaller than the smallest thing. Yet all the worlds and everyone in them rest on it. It cannot be destroyed. It is the life-breath, speech and mind, and it is true and immortal. The teacher tells his student: aim at it and hit it.