[LII. Ben.]
Of the words of Matthew 3:13, “Then Jesus comes from Galilee to the Jordan unto John, to be baptized of him.” Concerning the Trinity.
1. The lesson of the Gospel has set before me a subject whereof to speak to you, beloved, as though by the Lord's command, and by His command in very deed. For my heart has waited for an order as it were from Him to speak, that I might understand thereby that it is His wish that I should speak on that which He has also willed should be read to you. Let your zeal and devotion then give ear, and before the Lord our God Himself aid ye my labour. For we behold and see as it were in a divine spectacle exhibited to us, the notice of our God in Trinity, conveyed to us at the river Jordan. For when Jesus came and was baptized by John, the Lord by His servant (and this He did for an example of humility; for He shows that in this same humility is righteousness fulfilled, when as John said to Him, “I have need to be baptized by You, and You come to me?” He answered, “Suffer it to be so now, that all righteousness may be fulfilled”), when He was baptized then, the heavens were opened, and the Holy Spirit came down upon Him in the form of a Dove: and then a Voice from on high followed, “This is My beloved Son, in whom I am well pleased.” Here then we have the Trinity in a certain sort distinguished. The Father in the Voice,— the Son in the Man—the Holy Spirit in the Dove. It was only needful just to mention this, for most obvious is it to see. For the notice of the Trinity is here conveyed to us plainly and without leaving room for doubt or hesitation. For the Lord Christ Himself coming in the form of a servant to John, is doubtlessly the Son: for it cannot be said that it was the Father, or the Holy Spirit. “Jesus,” it is said, “comes;” that is, the Son of God. And who has any doubt about the Dove? Or who says, “What is the Dove?” when the Gospel itself most plainly testifies, “The Holy Spirit descended upon Him in the form of a dove.” And in like manner as to that voice there can be no doubt that it is the Father's, when He says, “You are My Son.” Thus then we have the Trinity distinguished.
Source: Sermons on Selected Lessons of the New Testament (New Advent)