The Baptism of Jesus

Last night at house group we were looking at the baptism of Jesus; a subject I have struggled with for years.  You see as a Baptist I view baptism as a sacrament that symbolises the believers new life in Christ; they symbolically die to their sin as they are immersed in the water and rise into their new Christian life.  That is fine for the here and now but why did the sinless Jesus have to be baptised?

I suspect the answer is that we view faith as an individual issue but in first century Palestine the community (corporate?) was important as well.  As far as we can know from the Gospels Jesus lived a very ordinary life between the ages of 12 and 30 in a society which, like all the rest of its members, would have been sinful.  As Jesus sets out on His ministry he leaves the life of a carpenter behind and separates Himself from the sinful society in which He had lived.  His baptism is therefore symbolic of Him moving out from His former life in society to take on fully His role as the perfect Son of God.

Any other ideas?