8 Yet the Lord also has not left us to chance, since, in that He said, “The Son cannot of Himself do anything, but what He sees the Father doing,” He meant us to understand that the Father does, not some works which the Son may see, and the Son does other works after He has seen the Father doing; but that both the Father and Son do the very same works. For He goes on to say, “For what things soever He does, these also does the Son in like manner.” Not after the Father has done works, does the Son other works in like manner; but, “whatever He does, these also the Son does in like manner.” If these the Son does which the Father does, then it is by the Son that the Father does: if by the Son the Father does what He does, then the Father does not some, the Son others; but the works of the Father and of the Son are the same works. And how does the Son also the same? Both “the same,” and “in like manner.” In case you should think them the same, but in a different manner, the “same,” says He, and “in like manner.” And how could they be the same and not in like manner? Take an example, which I presume is not too big for you: when we write letters they are first formed by our heart, then by our hand. Certainly: why otherwise have you all agreed, but because you perceived it to be so? It is as I have said, it is manifest to us all. The letters are made first by our heart, then by our body; the hand serves, the heart commands; both the heart and the hand make the same letters. Do you think the heart does some letters, the hand some others? The same indeed does the hand, but not in like manner: our heart forms them intelligibly, but our hand visibly. See how the same things are made, but not in like manner. Hence it was not enough for the Lord to say, “What things soever the Father does, these also the Son does;” He must add, “and in like manner.” For what if you should understand this just as you understand whatever your heart does, this also your hand does, but in a different manner? Here, however, he added, “These also the Son does in like manner.” If He both does these, and in like manner does, then awake; let the Jew be crushed, let the Christian believe, let the heretic be convinced: The Son is equal to the Father.
9. “For the Father loves the Son, and shows Him all things that Himself does.” Here is that “shows.” “Shows,” as it were, to whom? Of course, as to one that sees. We return to that which we cannot explain, how the Word sees. Behold, man was made by the Word; but man has eyes, ears, hands, various members in the body: he is able by the eyes to see, by the ears to hear, by the hands to work; the members are diverse, their offices diverse. One member cannot do the office of another; yet, by reason of the unity of the body, the eye sees both for itself and for the ear, and the ear hears for itself and for the eye. Are we to suppose that something like this holds good in the Word, seeing all things are by Him; and Scripture has said in the psalm, “Understand, you brutish among the people; and you fools, at length be wise. He that planted the ear, shall He not hear? And He that formed the eye, shall He not see?” Hence, if the Word is He that formed the eye, for all things are by the Word; if the Word is He that planted the ear, for all things are by the Word: we cannot say the Word does not hear, the Word does not see; lest the psalm reprove us, and say, “Fools, at length be wise.” Therefore, if the Word hears and sees, if the Son hears and sees, are we yet to search for eyes and ears in Him in separate places? Does He by one part hear, by another see; and cannot His ear do what His eye does; and cannot His eye do what His ear can? Or is He not all sight, all hearing? Perhaps yes; nay, not perhaps, but truly yes; while, however, that seeing of His, and that hearing of His, is in a way far other than it is with us. Both to see and to hear exist together in the Word: seeing and hearing are not diverse things in Him; but hearing is sight, and sight is hearing.
Source: Tractates on the Gospel of John (New Advent)