3 I ask You, O Lord Christ, resolve the difficulty, put an end to the contention. “All things,” says He, “that the Father has are Mine.” Are they then not the Father's, if they are Yours? For He does not say, “All things that the Father has He has given unto Me;” although, if He had said even this, He would have shown His equality. But the difficulty is that He said, “All things that the Father has are Mine.” If you understand it aright, All things that the Father has, are the Son's; all things that the Son has, are the Father's.
Hear Him in another place; “All Mine are Yours, and Yours are Mine.” The question is finished, as to the things which the Father and the Son have: they have them with one consent, do not you introduce dissension. What He calls the works of the Father, are His Own works; for, “Yours too are Mine,” for He speaks of the works of That Father, to whom He said, “All Mine are Yours, and Yours are Mine.” So then, My works are Yours, and Your works are Mine. “For what things soever the Father does;” Himself has said, the Lord has said, the Only-Begotten has said, the Son has said, the Truth has said.
What has He said? “What things soever the Father does, these also does the Son in like manner.” Signal expression! signal truth! signal equality. “All things that the Father does, these does the Son also.” Were it enough to say, “All things that the Father does, these does the Son also”? It is not enough; I add, “in like manner.” Why do I add, “in like manner”? Because they who do not understand, and who walk with eyes not yet open, are wont to say, “The Father does them by way of command, the Son of obedience, therefore not in like manner.” But if in like manner, as the One, so the Other; so what things the One, the same the Other.
Source: Sermons on Selected Lessons of the New Testament (New Advent)