43 Now we ought to recognise first of all that God has spoken not for Himself but for us, and that He has so far tempered the language of His utterance as to enable the weakness of our nature to grasp and understand it. For after being rebuked by the Jews for having made Himself the equal of God by professing to be the Son of God, He had answered that He Himself did all things that the Father did, and that He had received all judgment from the Father; moreover that He must be honoured even as the Father.
And in all these things having before declared Himself Son, He had made Himself equal to the Father in honour, power and nature. Afterwards He had said that as the Father had life in Himself, so He had given the Son to have life in Himself, wherein He signified that by virtue of the mystery of the birth He possessed the unity of the same nature. For when He says that He has what the Father has, He means that He has the Father's self. For that God is not after human fashion of a composite being, so that in Him there is a difference of kind between Possessor and Possessed; but all that He is is life, a nature, that is, complete, absolute and infinite, not composed of dissimilar elements but with one life permeating the whole.
And since this life was in such wise given as it was possessed, although the fact that it was given manifestly reveals the birth of the Recipient, it yet does not involve a difference of kind since the life given was such as was possessed.
Source: On the Trinity (New Advent)