1 Samuel 16-19

Having rejected Saul as the king of Israel, the Lord sends Samuel to Bethlehem to find and anoint a new king. Directing Samuel to the house of Jacob, the Lord instructs Samuel to select one of Jacob's sons. In doing so, the Lord cautions Samuel:

Not as man sees does God see, because man sees the appearance but the Lord looks into the heart.

The Lord chooses David, the youngest of Jesse's sons, and Samuel anoints him. Soon after, because of is talents on the harp, David finds himself at Saul's side, playing soothing music to calm Saul when the evil spirit sent by the Lord is tormenting Saul. Saul becomes fond of David. When faced with a battle against the Philistines, Saul's army is terrified and their God insulted, by the giant, Goliath. Of all people, it is David who accepts the challenge to face Goliath one-on-one, saying:

I come against you in the name of the Lord of hosts, the God of the armies of Israel that you have insulted. Today, the Lord shall deliver you into my hand; I will strike you down and cut off your head.

And so he does. With his slingshot, he fells Goliath and cuts off his head--sending the Philistines fleeing in terror and securing victory for the Israelites. 

From this event, many consequences ensue. Saul's son, Jonathan, becomes a great friend and admirer of David's, as fond of him as if his life depended on him. The people of Israel see David as a hero and literally sing his praises. He becomes the head of Saul's army and leads them to many victories. But Saul becomes increasingly jealous over time, to the point that he schemes to bring about David's death. After marrying one of Saul's daughters, David is ultimately forced to flee his home to avoid death at Saul's hands. David finds refuge with Samuel to escape Saul's persecution. Saul finds him even there in that hiding place, but Saul himself is overcome with the prophetic spirit that had enraptured Samuel, David, and the others staying with them.

The Lord helps David, a handsome but otherwise ordinary seeming man, become a great hero, filling him with the spirit of the Lord. With that spirit, David--and all of us--can surely do great things.