15 Behold, He has named eternal life. Has He told us that we shall there see and know the Father and Son? What if we shall live for ever, yet not see that Father and Son? Hear, in another place, where He has named eternal life, and expressed what eternal life is: “Be not afraid; I do not deceive you; not without cause have I promised to them that love me, saying, 'He that has my commandments, and keeps them, he it is that loves me; and he that loves me, shall be loved of my Father, and I will love him, and will show myself to him.'” Let us answer the Lord, and say, What great thing is this, O Lord our God?
What great thing is it? Will You show Yourself to us? What, then, did You not show Yourself to the Jews also? Did not they see You who crucified You? But You will show Yourself in the judgment, when we shall stand at Your right hand; will not also they who will stand on Your left see You? What is it that You will show Yourself to us? Do we, indeed, not see You now when You are speaking? He makes answer: I will show myself in the form of God; just now you see the form of a servant.
I will not deceive you, O faithful man; believe that you shall see. You love, and yet you do not see: shall not love itself lead you to see? Love, persevere in loving; I will not disappoint your love, says He, I who have purified your heart. For why have I purified your heart, but to the end that God may be seen by you? For “blessed are the pure in heart, for they shall see God.” “But this,” says the servant, as if disputing with the Lord, “You did not express, when Thou said, 'The righteous shall go into life eternal;' You did not say, They shall go to see me in the form of God, and to see the Father, with whom I am equal.” Observe what He said elsewhere: “This is life eternal, that they may know You the one true God, and Jesus Christ whom You have sent.”
Source: Tractates on the Gospel of John (New Advent)