11 Afterwards, because He was made man, what gave He to Him? “And has given Him authority to execute judgment, because He is the Son of man.” In that He is the Son of God, “As the Father has life in Himself, so also has He given to the Son to have life in Himself;” in that He is the Son of man, “He has given Him authority of executing judgment.” This is what I ex plained to you yesterday, my beloved, that in the judgment man will be seen, but God will not be seen; but after the judgment, God will be seen by those who have prevailed in the judgment, but by the wicked He will not be seen.
Since, therefore, the man will be seen in the judgment in that form in which He will so come as He ascended, for that reason He had said above, “The Father judges not any man, but has given all judgment to the Son.” He repeats the same thing also in this place, when He says, “And has given Him authority of executing judgment, because He is the Son of man.” As if you were to say, “has given Him authority of executing judgment.” In what way? When He had not that authority of executing judgment?
Since “in the beginning was the Word, and the Word was with God, and the Word was God;” since “all things were made by Him,” did He not already have authority of executing judgment? Yes, but according to this, I say, “He gave Him authority of executing judgment, because He is the Son of man:” according to this, He received authority of judging “because He is the Son of man.” For in that He is the Son of God, He always had this authority. He that was crucified, received; He who was in death, is in life: the Word of God never was in death, but is always in life.
Source: Tractates on the Gospel of John (New Advent)