At first blush it seems odd that the student is baptizing the master. But John is a conduit. He is simply performing the ritual. The reasons for Jesus' submission are far deeper and to the heart of overall mission. He is baptized for these reasons: 

1. To fulfill all Righteousness: To be consecrated to God and approved by God.
2. The public announcement of the arrival of the Messiah and the inception of His ministry.
3. Identification with human sin and identification of himself with the peoples movement toward God.
4. To be an example to his followers.