John's baptism was all about repenting and confessing sins and humbly expressing their need of God’s forgiveness.  People came to John because they knew they were not spiritually clean.  They knew they were not ready to meet God's Messiah: so they came to be baptised.  But why would Jesus come?  He had done no wrong and John knew it, asking the same question.  Although he was baptising, he knew that he was also a sinner in need of God's forgiveness.  So, John suggested that Jesus should baptise him.

But Jesus persisted.  It was necessary, He said, to please God and do what He required.  Of course, Jesus could not confess His own sin because He had done nothing wrong.  He was not a sinner; but he identified Himself with sinners.  One way of looking at it was that Jesus shared the dirty bath-water of the sinners who came to be baptised.  

Very soon He would carry the weight of all the sins of the world, in His body.  His baptism was a prophetic action which looked forward to the cross when He was 'numbered with the transgressors' (Isaiah 53:12; Luke 22:37).

Jesus kept on surprising people because they did not expect Him to be different to them.  But He was God, and God's ways are different to ours.  Isaiah 55:9 says, "As the heavens are higher than the earth, so are my ways higher than your ways and my thoughts than your thoughts."  We would not have thought of God coming to live as a man, or for Him to accept responsibility for the sins of the world and be punished for them.  But God's ways are different to ours.  What is right to God may seem very strange to us, but that does not mean it is wrong.  So do not judge God's ways by human logic or expect God to conform to human expectations.  Indeed, we should expect that God's ways, methods, timings, destinations and routes will be higher and better and more complete than we might ever have imagined.