Baptism for me, is an act of obedience, it is symbolic of the gospel and has nothing (literally) to do with washing away of sins. If it did, why was Jesus baptized?
Obviously Mark's narrative which simply had Jesus baptised by John (implying, from v. 4, "baptism of repentance for the forgiveness of sins") was quite embarrassing to others:
(1) Matthew adds an awkward explanation:
Then Jesus came from Galilee to John at the Jordan, to be baptized by him. John would have prevented him, saying, "I need to be baptized by you, and do you come to me?" But Jesus answered him, "Let it be so now; for it is proper for us in this way to fulfill all righteousness." Then he consented.
(2) Luke avoids the direct connection between Jesus' baptism and John by having the latter put into prison before mentioning Jesus baptism, incidentally, with "all the people".
(3) John suppresses any mention of Jesus' baptism.