4 How much soever then we may understand, and how much soever we may see, we shall not see as the Son sees, even when we shall be made equal with the angels. For we are something even when we do not see; but what are we when we do not see, other than persons not seeing? And that we may see, we turn to Him whom we may see, and there is formed in us a seeing which was not before, although we were in being. For a man is when not seeing; and the same, when he does see, is called a man seeing.
For him, then, to see is not the same thing as to be a man; for if it were, he would not be man when not seeing. But since he is man when not seeing, and seeks to see what he sees not, he is one who seeks, and who turns to see; and when he has well turned and has seen, he becomes a man seeing, who was before a man not seeing. Consequently, to see is to him a thing that comes and goes; it comes to him when he turns to, and leaves him when he turns away. Is it thus with the Son?
Far be it from us to think so. It was never so that He was Son, not seeing, and afterwards was made to see; but to see the Father is to Him the same thing as to be Son. For we, by turning away to sin, lose enlightenment; and by turning to God we receive enlightenment. For the light by which we are enlightened is one thing; we who are enlightened, another thing. But the light itself, by which we are enlightened, neither turns away from itself, nor loses its lucidity, because as light it exists.
The Father, then, shows a thing which He does to the Son, in such wise that the Son sees all things in the Father, and is all things in the Father. For by seeing He was begotten; and by being begotten He sees. Not, however, that at any time He was not begotten, and afterwards was begotten; nor that at any time He saw not, and afterwards saw. But in what consists His seeing, in the same consists His being, in the same His being begotten, in the same His continuing, in the same His unchanging, in the same His abiding without beginning and without end.
Let us not therefore take it in a carnal sense that the Father sits and does a work, and shows it to the Son; and the Son sees the work that the Father does, and does another work in another place, or out of other materials. For “all things were made by Him, and without Him was nothing made.” The Son is the Word of the Father. The Father said nothing which He did not say in the Son. For by speaking in the Son what He was about to do through the Son, He begot the Son through whom He made all things.
Source: Tractates on the Gospel of John (New Advent)