In the story line of 1 Samuel, the encounter of David and Goliath contrasts the worldview of David with that of King Saul. God has chosen Saul to be the king the people thought they wanted. Standing head and shoulders above his peers, Saul is the one who is supposed to lead the people into battle. While the conversation between David and the giant is significant to the story, the one between David and Saul is crucial. It appears this story is taken out of chronological order (the general arrangement of the book). The narrator has already introduced David’s presence in Saul’s court when he comes to play the harp. David has already been anointed to be the next king in an earlier overview section.
The conflict with the Philistines and especially with Goliath reveals a fundamental difference between Saul and David–their views of God and how that affects their approach to warfare against their enemies. Saul relies on himself and his armor. Often the artwork illustrating this scene presents a boy who is twelve or younger foolishly trying to mimic an adult. Saul’s actions, though, are not foolish because David is too small, the issue is contained in the question, “In what/whom are you trusting?”
From the Desk of John King 
John, thank you. I thought as I read your words that like Saul with David, sometimes our efforts to protect others actually prevent them from healthy growth and adventure. David possessed enough confidence in God and was comfortable enough in his own worldview to chart his own course of action.
So true! David’s healthy view of himself arose from his view of God, just as Saul’s fear arose from his unhealthy view.