This is my beloved Son, with whom I am well pleased. Today the Church commemorates the event of the baptism of Jesus by his cousin John the Baptist in the river Jordan. It is a feast that not only continues our celebration of the  unveiling of Jesus Christ as the fullness of God’s revelation to the world (Epiphany), but also brings to a culmination the mysteries of the Incarnation of the Son of God that we have been celebrating during these days of Christmas. Whereas Jesus’ baptism took place some thirty or so years after his birth (cf. Luke 3:23), its commemoration takes place as a conclusion of the season of Christmas. Since it is the event of Jesus’ baptism that marked the beginning of his ministry, the Ordinary time that is ushered today (this Sunday also serves as the First Sunday in Ordinary Time) will be a time for us to celebrate the implication of the event of the Incarnation: God reaching out to save us. 
On this feast of the baptism of Jesus, we celebrate the divine consecration of Jesus as the Father’s beloved. It is a consecration which reveals Jesus’ divine mission (initiating us into the mysteries of our salvation) for it is during his baptism that God made a “formal” presentation of Jesus to the world ( this is my beloved Son with whom I am well pleased). As we learn from the Gospel accounts, the baptism of Jesus not only marked the end of the “hidden life at Nazareth” but more importantly thrust him into public ministry. And since it is into this very baptism of Jesus that we too are baptized, our post-baptism mission becomes that of joining Jesus in his salvific ministry. It is in the baptism of Jesus that the salvation of the universe lies. 
The baptism of Jesus was very integral to his mission. Although as Son of God Jesus did not require baptism (John’s baptism was for repentance and forgiveness of sins [cf. Mark 1:4]), he allowed himself to be baptized in order that he could become a model for imitation by his brothers and sisters. It was for this reason that when John became hesitant to baptize him, it was Jesus himself who urged him to proceed with the baptism, telling him it was fitting (cf. Matthew 3:14-15). Jesus understood that his baptism by John was “necessary” since his own ministry would be built upon John’s. The baptism of John was requisite for the turning away from sin which then allowed one to be receptive to the message of the the kingdom that would be the subject of Jesus’ preaching ministry. And although baptism by Jesus would take on a more different approach (cf. Mark 1:8), it nonetheless remained an integral part of Jesus ministry (and of the movement that he founded). For as Jesus was getting ready to ascend back to the father, his last instruction to the apostles was that they go to all the corners of the world in order to baptize (cf. Matthew 28:19). Without baptism, the mission of Jesus (salvation of the world) becomes hindered.   
Our own baptism is patterned after that of Jesus (we are baptized in the name of Jesus). Consequently, when we are baptized, we join Jesus in his mission of saving the world since through our baptism, we “assume” the identity of Jesus. This is because in baptism, we become new creatures, creatures that have regained the likeness of God, a likeness we lost when our first parents rebelled against God. A new creature is one who has learned how to love again, a creature who has learned how to live in a community (for baptism inserts us into the community of Christ’s body). Thus baptized, we find ourselves thrust into this body/community of believers, and as such we have to live as a people who are living with others. In our old selves, we lived selfish lives, lives in which we were the only ones, lives in which we were the center of attention. Now as new creatures, we learn to look around and realize that we live in a community, that we are part of a big picture. St. Paul reminds us that after we are baptized, we no longer live for ourselves, but for God and for members of the body of Christ (cf. I Corinthians 12:1ff). After baptism, the "I" in us dies off, and is replaced by a "we." Immediately after baptism, one is called to be subject to others, to serve them in the communion of the Church.
And so today as we celebrate the baptism of our Lord, we are invited to renew our baptismal promises and continue living as the new creatures that we have become.