I heard a great teaching on why John baptized Jesus. John came from the Levitical line while Jesus came from the tribe of Judah. As a Levitical priest, one of the jobs was to wash the sacrifice. Jesus came to fulfill all righteousness. John washed Jesus as the sacrifice of sacrifices.
The Baptism of Jesus
13Then Jesus arrived from Galilee at the Jordan coming to John, to be baptized by him.
14But John tried to prevent Him, saying, “I have need to be baptized by You, and do You come to me?”
15But Jesus answering said to him, “Permit it at this time; for in this way it is fitting for us to fulfill all righteousness.” Then he permitted Him.
16After being baptized, Jesus came up immediately from the water; and behold, the heavens were opened, and he saw the Spirit of God descending as a dove and lighting on Him,
17and behold, a voice out of the heavens said, “This is My beloved Son, in whom I am well-pleased.”