20 And next, lest it should seem that to give life to whom He will is not within the power of One Who has been truly born, but is only the prerogative of ingenerate Omnipotence, He hastens to add, For the Father judges no man, but has given all judgment to the Son. The statement that all judgment is given teaches both His birth and His Sonship; for only a nature which is altogether one with the Father's could possess all things; and a Son can possess nothing, except by gift.
But all judgment has been given Him for He quickens whom He will. Now we cannot suppose that judgment is taken away from the Father, although He does not exercise it; for the Son's whole power of judgment proceeds from the Father's, being a gift from Him. And there is no concealment of the reason why judgment has been given to the Son, for the words which follow are, But He has given all judgment to the Son, that all men may honour the Son even as they honour the Father. He that honours not the Son honours not the Father Which has sent Him.
What possible excuse remains for doubt, or for the irreverence of denial? The reason for the gift of judgment is that the Son may receive an honour equal to that which is paid to the Father; and thus he who dishonours the Son is guilty of dishonouring the Father also. How, after this proof, can we imagine that the nature given Him by birth is different from the Father's, when He is the Father's equal in work, in power, in honour, in the punishment awarded to gainsayers? Thus this whole Divine reply is nothing else than an unfolding of the mystery of His birth. And the only distinction that it is right or possible to make between Father and Son is that the Latter was born; yet born in such a sense as to be One with His Father.
Source: On the Trinity (New Advent)