The Baptism of the Lord

And when Jesus had been baptized, just as he came up from the water, suddenly the heavens were opened to him and he saw the Spirit of God descending like a dove and alighting on him. And a voice from heaven said, ‘This is my Son, the Beloved, with whom I am well pleased.’

Another of a series of five major manifestations of Christ's divine nature that we find in the Gospels (The Nativity, The Epiphany, The Wedding Feast at Cana, The Transfiguration, being the others) this feast at one point was a part of a single celebration that included the Nativity and Epiphany as well.

As our Christmas season draws to a close, we find Christ approaching a baptism for the forgiveness of sins, a baptism of which he has no need. yet he tells John in the midst of his protests that it must be so. As we've seen so often before in the scriptures, waters are opened, God is made manifest, and the Word proclaims a message of hope and wonder "This is my Son, the beloved..."

Trhough the pouring out of the Holy Spirit, this beloved Son joins himself with our human state that we might be joined with his. We are reminded of this at every single Mass as we are called to witness at the start of our Eucharistic Liturgy, the priest adding water to wine and humbly praying, "By the mystery of this water and wine may we come to share in the divinity of Christ who humbled himself to share in our humanity"

More on the Baptism of the Lord (From catholicism.about.com);

The Baptism of the Lord has historically been associated with the celebration of Epiphany. Even today, the Eastern Christian feast of Theophany, celebrated on January 6 as a counterpart to the Western feast of Epiphany, focuses primarily on the Baptism of the Lord as the revelation of God to man.

After the Nativity of Christ (Christmas) was separated out from Epiphany, the Church in the West continued the process and dedicated a celebration to each of the major epiphanies (revelations) or theophanies (the revelation of God to man): the Birth of Christ at Christmas, which revealed Christ to Israel; the revelation of Christ to the Gentiles, in the visit of the Wise Men at Epiphany; the Baptism of the Lord, which revealed the Trinity; and the miracle at the wedding at Cana, which revealed Christ's transformation of the world. (For more on the four theophanies, see the article on Christmas.)

Thus, the Baptism of the Lord began to be celebrated on the octave (eighth day) of Epiphany, with the miracle at Cana celebrated on the Sunday after that. In the current liturgical calendar, the Baptism of the Lord is celebrated on the Sunday after January 6, and, a week later, on the Second Sunday of Ordinary Time, we hear the Gospel of the Wedding at Cana.

Prayer From the Liturgy of the Hours (Divine Office) for the Baptism of the Lord;
Almighty, eternal God,
when the Spirit descended upon Jesus
at his baptism in the Jordan,
you revealed him as your own beloved Son.
Keep us, your children born of water and the Spirit,
faithful to our calling.
We ask this through our Lord Jesus Christ, your Son,
who lives and reigns with you and the Holy Spirit,
one God for ever and ever. Amen.

Peace and God Bless