
Augustine of Hippo
Catena Aurea · Johannesevangelium 1
And John bare record, saying, I saw the Spirit descending from heaven like a dove, and it abode upon him. And I knew him not: but he that sent me to baptize with water, the same said unto me, Upon whom thou shalt see the Spirit descending, and remaining on him, the same is he which baptizeth with the Holy Ghost. And I saw, and bare record that this is the Son of God.
(Tr. vii. in Joan) It was necessary that the Only Son of God should baptize, not an adopted son. Adopted sons are ministers of the Only Son: but though they have the ministration, the Only one alone has the power.