From today's Office of Readings: A sermon by St. Gregory Nazianzen

John is baptising when Jesus draws near. Perhaps he comes to sanctify his baptiser; certainly he comes to bury sinful humanity in the waters. He comes to sanctify the Jordan for our sake and in readiness for us; he who is spirit and flesh comes to begin a new creation through the Spirit and water.
The Baptist protests; Jesus insists. Then John says: I ought to be baptised by you. He is the lamp in the presence of the sun, the voice in the presence of the Word, the friend in the presence of the Bridegroom, the greatest of all born of woman in the presence of the firstborn of all creation, the one who leapt in his mother’s womb in the presence of him who was adored in the womb, the forerunner and future forerunner in the presence of him who has already come and is to come again. I ought to be baptised by you: we should also add, “and for you”, for John is to be baptised in blood, washed clean like Peter, not only by the washing of his feet.
Jesus rises from the waters; the world rises with him. The heavens like Paradise with its flaming sword, closed by Adam for himself and his descendants, are rent open. The Spirit comes to him as to an equal, bearing witness to his Godhead. A voice bears witness to him from heaven, his place of origin. The Spirit descends in bodily form like the dove that so long ago announced the ending of the flood and so gives honour to the body that is one with God.
Hymns of the Feast from the Greek Festal Menaion
Apolytikion: (First Tone)
Lord, when You were baptized in the Jordan, the worship of the Trinity was made manifest. For the voice of the Father gave witness to You, calling You Beloved; and the Spirit, in the form of a dove, confirmed the certainty of His words. Glory to You, Christ our God, who appeared and enlightened the world.
Kontakion: (Fourth Tone)
Today You appeared to the world, and Your light, O Lord, has left its mark upon us as in fuller understanding we sing to You: “You came, You were made manifest, the unapproachable light.”
From the Liturgy of the Hours: Morning Prayer Antiphons
Antiphon 1: The Soldier baptizes his King, the servant his Lord, John his Savior; the waters of Jordan tremble, a dove hovers as a sign of witness, and the voice of the Father is heard: This is my Son.
Antiphon 2: Springs of water were made holy as Christ revealed his glory to the world. Draw water from the fountain of the Savior, for Christ our God has hallowed all creation.
Antiphon 3: You burned away man's guilt by fore and the Holy Spirit. We give praise to you, Our God and Redeemer.
Gospel Canticle Antiphon: Christ is baptized, the world is made holy, he has taken away our sins. We shall be purified by water and the Holy Spirit.