47 Although we have treated this passage as the facts themselves explain it, yet to prove that the Lord's words, The Son can do nothing of Himself, but what He has seen the Father doing, so far from supporting this unholy degradation of His nature, testify to His conscious possession of the nature of the Father, by Whose authority He worked on the Sabbath, let us show them that we can produce another saying of the Lord, which bears upon the question, I do nothing of Myself, but as the Father taught Me, I speak these things.
And He that sent Me is with Me: He has not left Me alone, for I do always the things that are pleasing to Him. Do you feel what is implied in the words, The Son can do nothing, but what He has seen the Father doing? Or what a mystery is contained in the saying, I can do nothing of myself, and He has not left me alone, for I do always the things that are pleasing to Him? He does nothing of Himself, because the Father abides in Him; can you reconcile with this the fact that the Father does not leave Him, because He does the things which are pleasing to Him?
Your interpretation, heretic, sets up a contradiction between these two statements, that He does nothing of Himself, unless taught of the Father abiding in Him, and that the Father abides in Him, because He does always the things which are pleasing to Him. For if the Father's abiding in Him means that He does nothing of Himself, how could He have deserved that the Father should abide in Him, by doing always the things which are pleasing to the Father. It is no merit, not to do of oneself what one does.
Conversely, how are the Son's deeds pleasing to the Father, if the Father Himself, abiding in the Son, be their Author? Impiety, you are in a sore strait; the well-armed piety of the faith has hemmed you in. The Son is either an Agent, or He is not. If He is not an Agent, how does He please by his acts? If He is an Agent, in what sense are deeds, done not of Himself, His own? On the one hand, He must have done the things which are pleasing; on the other, it is no merit to have done, yet not of oneself, what one does.
Source: On the Trinity (New Advent)