6 Withdraw, then, from this wisdom of the flesh, and let us inquire in what manner it is said, “The Son cannot of Himself do anything, but what He sees the Father doing.” Let us inquire, if we are worthy to apprehend. For I confess it is a great thing, and altogether difficult; to see the Father doing through the Son: not the Father and the Son doing each His particular works, but the Father doing every work whatsoever by the Son; so that not any works are done by the Father without the Son, or by the Son without the Father, because “all things were made by Him, and without Him was nothing made.”
These truths being most firmly established in the foundation of faith, what now is the nature of this “seeing”? You seek, as I suppose, to know the Son doing: seek first to know the Son seeing. For what, in fact, says He? “The Son cannot of Himself do anything, but what He sees the Father doing.” Note what He said, “but what He sees the Father doing.” The seeing comes first, the doing follows: He sees in order to do. As for you, why do you seek at present to know how He does, while you understand not as yet how He sees?
Why do you run to that which comes later, leaving that which comes first? He declares Himself as seeing and doing, not doing and seeing; because “He cannot of Himself do anything, but what He sees the Father doing.” Will you that I explain to you how He does? Explain to me how He sees. If you can not explain this, neither can I that. If you are not yet competent to understand this, neither am I to understand that. Wherefore let each of us seek, each knock, that each may merit to receive.
Why do you, as if you were learned, unjustly blame me who am unlearned? I in respect of the doing, you in respect of the seeing, being both unlearned, let us inquire of the Master, not childishly wrangle in His school. We have already, however, learned together that “all things were made by Him.” Therefore it is manifest that it is not a different kind of works that the Father does, that, seeing them, the Son may do other works like them; but the very same does the Father by the Son, because all things were made by the Word.
Now, as to how God does, who knows? How made He, I will not say the world, but your own eye, in your carnal attachment to which you compare visible things with invisible? For you conceive of God such things as you are wont to see with these eyes. But if God might be seen with these eyes, He would not have said, “Blessed are the pure in heart, for they shall see God.” Accordingly, you have an eye of the body to see an artificer, but you have not yet the eye of the heart to see God: hence, what you are wont to see in an artificer, you would transfer to God. Leave earthly things on the earth; set your heart on high.
Source: Tractates on the Gospel of John (New Advent)