A father may therefore tell that doctrine of Brahman to his eldest son, or to a worthy pupil. But no one should tell it to anybody else, even if he gave him the whole sea-girt earth, full of treasure, for this doctrine is worth more than that, yea, it is worth more.

In plain words: So a father should teach this knowledge of Brahman only to his eldest son or a worthy student. He should not give it to anyone else, even for the whole treasure-filled earth, because it is worth more than all of that.