This is my beloved Son. My favor rests on him. Today the Church commemorates the baptism of Jesus by John in the river Jordan. It is a feast that brings to a culmination the mysteries of the Incarnation of the Son of God that we have been celebrating during these days of Christmas. This is because the baptism of the Lord is one of the two feasts of Christmas (the other being the Epiphany) in which we celebrate Jesus’ unveiling as the full revelation of God. In this feast of the baptism of the Lord, we celebrate the divine consecration of Jesus as the Father’s beloved. It is a consecration which reveals Jesus’ divine mission (the mission of 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 as he declared him as his beloved. As we learn from the Gospels, 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 in this very baptism of Jesus that we too are baptized, our post-baptism mission is that of joining Jesus in his salvific duty (it is in the baptism of Jesus that the salvation of the universe lies).
The baptism of Jesus was very integral to the mission of Jesus. Jesus was to “take over” from John the Baptist (cf. John 3:30: “he must increase, but I must decrease…”), and it was fitting that he be baptized by John so that he could become a model for us to imitate (when John became hesitant to baptize Jesus, and rightly so, Jesus replied: “Leave it like this for the time being; it is fitting that we should, in this way, do all that uprightness demands” cf. Matthew 3:15). John’s baptism was requisite for the turning away from sin in order to belong to the kingdom of God that Jesus was soon to inaugurate. It was the one single ritual that all those who were heeding his call had to undergo. And although baptism by Jesus would later on take on a more different approach, it nonetheless remained as well 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, for at our baptism we “assume” the identity of Jesus. This is because in baptism, we become new creatures. In other words, baptism enables us to regain our likeness to God that is lost whenever we decide to turn away from God. As new creatures, the baptized learn how to live once again as members of a community. Baptism does away with selfish habits that tend to destroy communal living. Having clothed themselves with Christ, the baptized acquire the personality of Jesus. They learn to love, be kind, practice charity, forgive, and to live for others to the point of willing to die for them. It is only then that Jesus’ mission of setting the world on the path to salvation can be realized. It is the baptized who must carry on this mission of Jesus. And they can do it because they have learned to live as creatures of love.