God sent a troubling / distressing spirit to Saul for disobeying Him. Samuel anointed David king. David had a personality that attracted people and won their confidence in him. David came to play the harp to soothe Saul. The evil spirit departed from Saul when David played. David went out and killed Goliath, seeing this as a conflict between the true God of Israel and the false gods of the Philistines. David went to Jerusalem and put Goliath's head at the gate to tell the Jebusites judgement is coming to Jerusalem, leaving his armor in his tent. Jonathan loved David and made a covenant with David. Did he know David was going to be the king being he would have been the heir to the throne?
What can we learn from David behaving himself wisely?
David feared God and believed God and God gave him wisdom.
David remained faithful to Saul while he remained king because he was the Lord's annointed.
David was contrite before God, enabling God to use him.
David was a steady, Spirit controlled person.
David learned patience while being pursued by Saul in the wilderness.