So why was Jesus baptized? For us! In His baptism, Jesus identified fully with our humanity. What Jesus redeemed - us from sin - he fully identified with through his humanity, which He made clear by submitting to baptism by John. Further, Jesus' baptism marked the initiation of His public ministry, which eventually led to the cross. The Apostle John points out that Jesus came by water and by blood, the water representing His baptism and the blood representing His death on the cross.
At His baptism, Jesus was confirmed as the Son of God through the sign of the Holy Spirit descending on Him as a dove and by God the Father audibly speaking, "This is my beloved Son, in whom I am pleased." The Trinity was fully present at Jesus' baptism.
Jesus' baptism was so important that the Church recognizes baptism as one of her sacraments. A sacrament is an outer sign, such as water in the case of baptism, of an inward grace, our union with Christ through our baptism as we are accepted as members of His body, the Church. What is required of us? Repentance from sin and belief in Jesus as our Savior. We baptize infants, recognizing their membership in Christ's body and making the commitment to mentor them in the faith.