9 He does not say then, “What things soever the Father does, such does the Son:” as if the Father does some things, and the Son others. For it did seem as though He had meant this when He said above, “The Son does nothing of Himself, but what He sees the Father do.” Mark; He did not there either say, “But what He hears the Father enjoin;” but, “what He sees the Father do.” If then we consult the carnal understanding, or sense rather, He has set before Him as it were two workmen, the Father and the Son, the Father working without seeing any, the Son working from seeing the Father.
This is still a carnal view. Nevertheless, in order to understand those things which are higher, let us not decline these lower and mean things. First, let us set something before our eyes in this way; let us suppose there are two workmen, father and son. The father has made a chest, which the son could not make, unless he saw the father making it: he keeps his mind on the chest which the father has made, and makes another chest like it, not the same. I put off for a while the words which follow, and now I ask the Arian; “Do you understand it in the sense of this supposition?
Hath the Father done something, which when the Son saw Him do, He too has done something like it? For do the words by which you are perplexed seem to have this meaning?” Now He does not say, “The Son can do nothing of Himself, but what He hears the Father enjoin.” But He says, “The Son can do nothing of Himself, but what He sees the Father do.” See, if you understand it thus; the Father has done something, and the Son attends that He may see what He Himself too has to do; and that, some other thing like that which the Father had done.
This which the Father has done, by whom has He done it? If not by the Son, if not by the Word, you have incurred the charge of blasphemy against the Gospel. “For all things were made by Him.” So then what the Father had done, He had done by the Word; if by the Word He had done it, He had done it by the Son. Who then is that other who attends, that He may do some other thing which he sees the Father do? You have not been wont to say that the Father has two sons: there is One, One Only-Begotten of Him.
But through His mercy, Alone as regards His Divinity and not Alone as regards the inheritance. The Father has made coheirs with His Only Son; not begotten them like Him of His Own Substance, but adopted them by Him out of His Own family. For “we have been called,” as Holy Scripture testifies, “into the adoption of sons.”
Source: Sermons on Selected Lessons of the New Testament (New Advent)