(Daniel Bonnell, The Baptism of the Christ)
Let it be so now; it is proper for us to do this to fulfill all righteousness.
After the story of Jesus staying behind in Jerusalem when he was twelve, we don't hear anything else about Him until He is around thirty years old and leaves home to find John the Baptist. Jesus is going to get baptized. But why? John made it clear that his baptism was for the repentance of sins. Jesus had never sinned and therefore had nothing for which to repent.
JESUS TELLS US WHY
John was possibly wondering the same thing when he said, "I am the one who needs to be baptized by You so why are You coming to me?" When Jesus replies, He tells us why He is being baptized: "It is proper for us to do this to fulfill all righteousness." What does that mean? Walvoord says in the Bible Knowledge Commentary (p.25):
The Law included no requirements for baptism, so Jesus could not have had in view anything pertaining to Levitical righteousness. But John's message was a message of repentance, and those experiencing it were looking forward to a coming Messiah who would be righteous and who would bring in righteousness. If Messiah were to provide righteousness for sinners, He must be identified with sinners. It was therefore in the will of God for Him to be baptized by John in order to be identified (the real meaning of the word "baptized") with sinners."
Jesus' baptism showed that He identified with sinners. His perfect righteousness would fulfill all the requirements of the Law for sinful humanity who could never hope to do so on their own. When Jesus came up out of the water, the heavens opened, and the Spirit of God descended on Him in the form of a dove. And a voice from heaven spoke; it was God the Father. He said, "This is My Son, whom I love. In Him I am well-pleased." What a beautiful picture of the Trinity. God the Father speaking words of love and pleasure to the Son, the Holy Spirit coming down and resting on Jesus, and Jesus, the Son of God, coming up out of the water. The dove resting on Jesus and the voice speaking from heaven confirmed to John the Baptist that Jesus was the One promised, the One he had been sent to pave the way for.
A PICTURE OF SALVATION
Something else we see in Jesus' baptism is a picture of the future work of the Father, Son, and Holy Spirit in salvation. The Father chose us before the foundation of the world to be holy and blameless (Ephesians 1:4); the Son came to seek and save the lost (Luke 19:10); and the Spirit convicts of sin, righteousness, and judgment (John 16:8).
Since Jesus identified Himself with us while we were still sinners, once saved, we will want to get baptized as a way of showing we are identifying ourselves with Christ; His death and resurrection. Going under the water represents Jesus' death, being under the water represents His burial, and coming up out of the water represents His resurrection.