7 The beloved generates love, and the light immaterial the light inaccessible. “This is my beloved Son,” He who, being manifested on earth and yet unseparated from the Father's bosom, was manifested, and yet did not appear. For the appearing is a different thing, since in appearance the baptizer here is superior to the baptized. For this reason did the Father send down the Holy Spirit from heaven upon Him who was baptized. For as in the ark of Noah the love of God toward man is signified by the dove, so also now the Spirit, descending in the form of a dove, bearing as it were the fruit of the olive, rested on Him to whom the witness was borne.
For what reason? That the faithfulness of the Father's voice might be made known, and that the prophetic utterance of a long time past might be ratified. And what utterance is this? “The voice of the Lord (is) on the waters, the God of glory thundered; the Lord (is) upon many waters.” And what voice? “This is my beloved Son, in whom I am well pleased.” This is He who is named the son of Joseph, and (who is) according to the divine essence my Only-begotten. “This is my beloved Son”— He who is hungry, and yet maintains myriads; who is weary, and yet gives rest to the weary; who has not where to lay His head, and yet bears up all things in His hand; who suffers, and yet heals sufferings; who is smitten, and yet confers liberty on the world; who is pierced in the side, and yet repairs the side of Adam.
Source: Discourse on the Holy Theophany (New Advent)