When we repent of our sins, God forgives us wholly and completely. We are made new. Baptism is a wonderful symbol of the new life God gives us when we repent and make Him Lord of our life.
By being baptized, we are making a physical expression of the new life God has placed inwardly in our hearts. The water symbolizes cleansing, and when we lay back to die to our old life, our sin, we are then brought up and cleansed. We are a new creation.