20 The same things are commanded in the Decalogue as we are commanded to observe; but the same promises are not made as to us. What is promised to us? Life eternal. “And this is life eternal, that they know You, the only true God, and Jesus Christ whom You have sent.” The knowledge of God is promised: that is, grace for grace. Brethren, we now believe, we do not see; for faith the reward will be to see what we believe. The prophets knew this, but it was concealed before He came.
For a certain lover sighing, says in the Psalms: “One thing have I desired of the Lord, that will I seek after.” And do you ask what he seeks? For perhaps he seeks a land flowing with milk and honey carnally, although this is to be spiritually sought and desired; or perhaps the subjection of his enemies, or the death of foes, or the power and riches of this world. For he glows with love, and sighs greatly, and burns and pants. Let us see what he desires: “One thing have I desired of the Lord, that will I seek after.” What is it that he does seek after? “That I may dwell,” says he, “in the house of the Lord all the days of my life.” And suppose that you dwell in the house of the Lord, from what source will your joy there be derived? “That I may behold,” says he, “the beauty of the Lord.”
Source: Tractates on the Gospel of John (New Advent)