"I need to be baptized by you, and do you come to me?" --Matt. 3:14
"Why was Jesus Baptized?" Every January the Church celebrates the Baptism of Jesus Christ, an event recorded in all four Gospels. But the question is often asked, “Why was Jesus Baptized?” Baptism, according to the Catechism of the Catholic Church (Paragraph 1279), “…includes the forgiveness of original sin and all personal sins, birth into new life by which man becomes an adoptive son of the Father, a member of Christ and a temple of the Holy Spirit.”
But Jesus was sinless and is eternally the Son of the Father. Even John the Baptist seems confused by what Jesus did. “John would have prevented Him, saying, ‘I need to be baptized by you, and do you come to me?’ But Jesus answered him, ‘Let it be so now; for thus it is fitting for us to fulfill all righteousness.’ Then he consented” (Matt. 3:14-15). In the context of Matthew, “righteousness” is a fulfillment of the Law.
So why was Jesus Baptized?
Emeritus Pope Benedict the XVI explains it beautifully: “The Significance of this event could not fully emerge until it was seen in light of the Cross and Resurrection. Descending into the water, the candidates for Baptism confess their sin and seek to be rid of their burden of guilt. What did Jesus do in this same situation? …Looking at the events in light of the Cross and Resurrection, the Christian people realized what happened: Jesus loaded the burden of all mankind’s guilt upon His shoulders; He bore it down into the depths of the Jordan. He inaugurated His public activity by stepping into the place of sinners. This inaugural gesture is an anticipation of the Cross……
The whole significance of Jesus’ Baptism, the fact that He bears “all righteousness,” first comes to light on the Cross: The Baptism is an acceptance of death for the sins of humanity, and the voice that calls out “This is my beloved Son” over the baptismal waters is an anticipatory reference to the Resurrection” (Benedict XVI, Jesus of Nazareth, Vol. 1).
For further reading on the Baptism of Christ see Catechism of the Catholic Church (Paragraph 536).