The baptism of Jesus by John gives opportunity to define a starting point to Jesus' ministry, to see a picture of the trinity, and to take a look at the topic of baptism.  Of course, John wasn't performing "Christian" (believer's) baptism and Jesus didn't need to repent. Yet, Christ was eventually to take on the sin's of the world so it was proper for him to identify with the sinners that were coming to John.

Study notes are here.