Superman is the classic Son of the Sun God, here to redeem humanity. That he chooses to live with us as ONE of us despite his alien heritage is a reflection of the modern tendency to look inward for God/Truth/Enlightenment/etc. Without the human identity, he would have no right helping us at all because he would have no way to understand us.

He went on a truth seeking journey, a mission to find out where he was going and how best to get there. He was his own spiritual physician, and healed himself with freedom to all perspectives. In a sense, he became "many different persons in order to become one person."