12 See in all that He said, how carefully the Lord tempers the pious acknowledgment of His debt, so that neither the confession of the birth could be held to reflect upon His divinity, nor His reverent obedience to infringe upon His sovereign nature. He does not withhold the homage due from Him as the Begotten, Who owed to His Author His very existence, but He manifests by His confident bearing the consciousness of participation in that nature, which belongs to Him by virtue of the origin whereby He was born as God.
Take, for instance, the words, He that has seen Me, has seen the Father also, and, The words that I say, I speak not from Myself. He does not speak from Himself: therefore He receives from His Author that which He says. But if any have seen Him, they have seen the Father also: they are conscious, by this evidence, given to show that God is in Him, that a nature, one in kind with that of God, was born from God to subsist as God. Take again the words, That which the Father has given unto Me, is greater than all, and, I and the Father are one. To say that the Father gave, is a confession that He received His origin: but the unity of Himself with the Father is a property of His nature derived from that origin.
Take another instance, He has given all judgment unto the Son, that all may honour the Son even as they honour the Father. He acknowledges that the judgment is given to Him, and therefore He does not put His birth in the background: but He claims equal honour with the Father, and therefore He does not resign His nature. Yet another example, I am in the Father, and the Father is in Me, and, The Father is greater than I. The One is in the Other: recognise, then, the divinity of God, the Begotten of God: the Father is greater than He: perceive, then, His acknowledgment of the Father's authority.
In the same way He says, The Son can do nothing of Himself but what He has seen the Father doing: for what things soever He does, these the Son also does in like manner. He does nothing of Himself: that is, in accordance with His birth the Father prompts His actions: yet what things soever the Father does, these the Son also does in like manner; that is, He subsists as nothing less than God, and by the Father's omnipotent nature residing in Him, can do all that God the Father does.
All is uttered in agreement with His unity of Spirit with the Father, and the properties of that nature, which He possesses by virtue of His birth. That birth, which brought Him into being, constituted Him divine, and His being reveals the consciousness of that divine nature. God the Son confesses God His Father, because He was born of Him; but also, because He was born, He inherits the whole nature of God.
Source: On the Trinity (New Advent)