Why did Jesus Need to be Baptized?

This is apparently a question that also puzzled the earliest Christians, who believed Jesus was the  sinless Son of God. So in Matthew 3.13-15, Jesus comes forward to be baptized, and John asks whether Jesus should not be the one baptizing John.  Jesus say, "Let it be so for now, for this it is fitting for us to fulfill all righteousness."  A mysterious saying!   But he seems to me to mean:  God's plan is that I should begin my ministry by wholly identifying myself with the people of Israel.

In John 1 31-34, the Baptist says he did not realize who Jesus was at first, and so baptized him with the rest.  Then he saw the Spirit descend on Jesus, and  realized Jesus' own mission was to baptize people in the Spirit - to lead them to share in his own Spirit-filled relationship to God.  So baptism by John meant something different from the baptism of Jesus, and from baptism by Jesus and his disciples; but Jesus begins as a Jewish man in the crowd.

In other words both passages seem to reflect the conviction of Jesus' disciples that his work was something like that of John - calling people to conversion and a new life -  but on a wholly different, new level.

"His baptism in this sense anticipates his subsequent submission to suffering and death because that too will be "what God wants" (see 26:39, 42, 44): and entrance into even deeper solidarity with sinful humankind to save them from their sins (1:21; see 20:28;26:28).  The "righteous" action of Jesus in submitting to baptism triggers a divine response that is a defining moment in the narrative of the Gospel (vv. 16-17)." (The Paulist Biblical Commentary, Paulist Press (September 3, 2018), page 916)