Baptism is an outward display to others of your acceptance of Christ as Lord of your life.  It is not necessary for salvation.  Jesus himself was baptized, and he had no need to be saved, for he had never sinned (see Matthew 3:13-17).  It shows an open obedience to God, hence the approval of the Father in verse 17, "This is my beloved Son, in whom I am well pleased."  Just as it pleased the Father concerning Jesus, it pleases the Father when we follow in believers baptism after we have trusted Christ as savior from the heart.  It is a display and memorial of Christ's death, burial, and resurrection (see Romans 6:1-5).