1 Samuel 17:40-41

He took his staff His shepherd's staff. These arms in themselves were contemptible, yet chosen by David, because he had no skill to use other arms; because he had inward assurance of the victory, even by these weapons; and because such a conquest would be more honourable to God, and most shameful and discouraging to the Philistines. He drew near Probably a signal was made that the Philistine's challenge was accepted. David, however, it seems, made the first motion toward him, to show he did not fear him.