The Lion Killer and the Bear Killer

Saul clothed David with his garments, put a bronze helmet on his head and he clothed them with armor. He girded his sword over his armor and tried to walk, for he had not tested them. The Philistine said to David, am I a dog that you come to me with sticks? Notice Goliath is distracted already by David's shepherd stick. If he's such a perfect slinger and cannot miss, why not just pick up one stone? It demonstrates that David has great faith, but not perfect faith.