Why did Jesus need to be baptised?
Jesus never sinned. I have always been confused about why he decided to receive baptism. I thought that perhaps it was to simply give us an example so that we would follow. The point in the story where Jesus is baptised though is basically at the end of John's ministry. John the Baptist has baptised all the people in Judea and Jerusalem, and then Jesus is basically last. So it wasn't really as an example for the people in his day.
John's baptism is for the forgiveness of sins, so this is still confusing. For the rest of us, we need to be forgiven of our sin. So what does baptism mean for us? For the rest of us it means a physical act of repentance. What is repentance? A decision to not sin in life. For those of us who have sinned in life (everyone except Jesus) this decision means leaving behind a sinful life, but also walking into a sinless life (of course we still struggle to be sinless). Think about it for a moment though- baptism is a covenant with God to live a sin free life. Jesus was able to make such a covenant. By getting baptised he was saying to the world "I am going on record to declare that I am living and will continue to live a sin free life before God, I covenant myself to be sin free." God's response to Jesus covenanting himself is immediate, "You are my son, who I love very much and I am very pleased with you."
Jesus covenanted himself to a sin free life. This is definitely an example, but it was a pre-requisite for his starting up the kingdom, his coronation if you like.
That's what baptism is for us, a covenant to be sin free before God and as such it is actually repentance in action. As such I can not see how a believer would not choose to take this physical step of making a covenant with God. It is an essential step in obedience to following Jesus.