17 And behold a voice from heaven, saying: This is my beloved Son, in whom I am well pleased.
Hilary: From these things thus fulfilled upon Christ, we might learn that after the washing of water the Holy Spirit also descends on us from the heavenly gates, on us also is shed an unction of heavenly glory, and an adoption to be the sons of God, pronounced by the Father’s voice.
Jerome: The mystery of the Trinity is shewn in this baptism. the Lord is baptized; the Spirit descends in the shape of a dove; the voice of the Father is heard giving testimony to the Son.
Ambrose, Ambrosiaster: And no wonder that the mystery of the Trinity is not wanting to the Lord’s laver, when even our laver contains the sacrament of the Trinity. The Lord willed to shew in His own case what He was after to ordain for men.
Pseudo-Augustine: Though Father, Son, and Holy Ghost are one nature, yet do thou hold most firmly that They be Three Persons; that it is the Father alone who said, “this is my beloved Son;” the Son alone over whom that voice of the Father was heard; and the Holy Ghost alone who in the likeness of a dove descended on Christ at His baptism.
Augustine: That the voice is that of the Father only is manifest from the words, “This is my Son.”
The Father loves the Son, but as a father should, not as a master may love a servant; and that as an own Son, not an adopted; therefore He adds, “in whom I am well-pleased.”
Remigius: If it be referred to the human nature of Christ, the sense is, I am pleased in Him, whom alone I have found without sin. Or according to another reading, “It hath pleased me” to appoint Him, by whom to perform those things I would perform, i.e. the redemption of the human race.
Scripture from the Douay-Rheims Bible. Commentary from St. Thomas Aquinas, Catena Aurea, Vol. I (London: Rivington, 1842).