If the Lord Jesus was without sin, why would He ever need to be baptized by John the Baptist?
The most direct answer to this question is that Jesus did not need to be baptized. So then, why did it happen? Let’s first look at what the Catechism of the Catholic Church says on the topic:
Our Lord voluntarily submitted himself to the baptism of St. John, intended for sinners, in order to "fulfill all righteousness." Jesus' gesture is a manifestation of his self-emptying. The Spirit who had hovered over the waters of the first creation descended then on the Christ as a prelude of the new creation, and the Father revealed Jesus as his "beloved Son." #1224
One way to think of Jesus’ baptism was that it is an anticipation of what He would do for us later on the cross. He would take upon Himself our sinfulness. Just as He did not die on the cross for His own sin, He did not receive the baptism of John to repent for His own sinfulness. We might rather say that Jesus made holy the waters of baptism by His own baptism. In addition, His Baptism in the Jordan River, like His Epiphany as a child to the magi, was another divine manifestation of Jesus’ true identity: “This is my beloved Son, with whom I am well pleased.” (Mt. 3:17)
Jesus’ Baptism should make us think about our own baptism. St. Paul’s words to the Romans are instructive:
Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? We were buried therefore with him by baptism into death, so that as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life. (Rom. 6:3-4)
Baptism gives us new life—eternal life. Baptism forgives our sinfulness—both original sin and any personal sin (once a person has reached the age of reason and is no longer an infant). With baptism we are adopted by God through Christ as His children. We become temples of God’s Holy Spirit dwelling within us. God’s own life now dwells in us—the life of sanctifying grace. We become a member of the mystical Body of Christ, the Church, and the doorway is now open for us to receive the other sacraments of the Church. All of these wonderful things and many other blessings (see the Catechism of the Catholic Church #1262ff.) occur with the simple pouring of water (or an immersion into it) combined with the baptismal formula: I baptize you in the name of the Father, and of the Son, and of the Holy Spirit.
Every time you bless yourself with holy water, remember that this sacramental is a reminder of your baptism into Christ Jesus who suffered and died for your salvation. I remind you to keep some in your homes.