Christ's treatment of the leper illustrates the point. Once he was approached by a leper, who knelt before him begging his help. God stamped leprosy as unclean, and using this as an object lesson, we may understand God's abhorrence of all the forms that sin takes. Leprosy was then a living death. It was a gradual and horrible dissolution, the body rotting out of the grave instead of in it.
Sin is like that.
It destroys a man before it destroys the body. Christians are made alive in Christ, a new creation. The leprosy of sin is truly dealt with. But a sick man forgiven of his sins could never be content to remain a sick man. Consider the paralytic man let down through the roof to reach Christ.