When Jesus asked John to baptize him, he did so in order to fulfill all righteousness. This was to show that Jesus was submitting to God's plan and fulfilling all that was required of him as the Messiah. Baptism was seen as a symbol of repentance and spiritual renewal, and Jesus' baptism marked the beginning of his public ministry. By undergoing baptism, Jesus demonstrated his identification with humanity and his willingness to take on the sins of the world. Thus, Jesus' request for baptism was not for himself, but rather to fulfill the requirements of God's plan for humanity.