David needed forgiveness. After David had lusted for Bathsheba, sinned with Bathsheba, deceived Uriah and murdered Uriah, he was in a very bad place. Having added “sin to sin,” he desperately needed God’s saving grace. 
But David asked for more than forgiveness. In Psalm 51, he immediately asked the Lord, “Blot out my transgressions. Wash me thoroughly from my iniquity, and cleanse me from my sin” (51:1-2). David wanted the sin, with its guilt, removed from his account. But then he went further than that. More than just pardon from past sins, David pleaded for the ability to keep himself from sinning again. He begged the Lord, “Create in me a clean heart” (51:10).
“Out of the heart” proceed “evil things” (Mark 7:21-23), so David asked that the Lord might create within him a clean heart that would not want to do these evils again. The next time we ask the Lord for forgiveness from past sins, let’s ask Him to create a clean heart that will not want to do those same sins again in the future.