David's heart

"Now it came to pass, when David was dwelling in his house, that David said to Nathan the prophet, 'see now, I dwell in a house of cedar, but the ark of the covenant of the Lord is under tent curtains.'” 1 Chronicles 17.1

 David committed sins that were not erased. Violent and unjustifiable sins. He  and his people reaped its fruits. However, even in the face of such outrage, his heart remained according to God's heart. The above verse proves that, for in his concern with the building of the House of the Lord, he considered his faith and covenant to the God of his forefathers.

MERCY

"Have mercy upon me, O God, according to Your lovingkindness, according to the multitude of Your tender mercies, blot out my transgressions."     Psalm 51.1

David's sin was extremely serious. However, every sin is deserving of forgiveness, as long as there is sincere repentance. 
David obtained repentance and forgiveness because of his sincere confession.
Today, the same mercy is available to all those who seek it. 

WAR

"Though an army may encamp against me, my heart shall not fear; though war may rise against me, in this I will be confident."      Psalm 27.3

David was a man of war and conquests because He trusted in his parent's God. He knew that God would never leave him alone. Confident is the key word in this verse. This is the kind of faith that pleases the Lord.