5 You will say, “This have I never seen, one begetting, and always with him whom he begot; but he that begot came first, and he that was begotten followed in time.” You say well, “I have never seen this;” for this appertains to “that which eye has not seen.” Do you ask how it may be expressed? It cannot be expressed; “For the ear has not heard, neither has it ascended unto the heart of man.” Be it believed and adored, when we believe, we adore; when we adore, we grow; when we grow, we comprehend.
For as yet while we are in this flesh, as long as we are absent from the Lord, we are, with respect to the Holy Angels who see these things, infants to be suckled by faith, hereafter to be fed by sight. For so says the Apostle, “As long as we are in the body we are absent from the Lord. For we walk by faith, not by sight.” We shall some day come to sight, which is thus promised us by John in his Epistle; “Dearly beloved, we are the sons of God, and it has not yet appeared what we shall be.” We are the sons of God now by grace, by faith, by the Sacrament, by the Blood of Christ, by the redemption of the Saviour; “We are the sons of God, and it has not yet appeared what we shall be. We know that when He shall appear, we shall be like Him, for we shall see Him as He is.”
Source: Sermons on Selected Lessons of the New Testament (New Advent)