When David steeped forward in faith to fight the Philistine giant, King Saul offered his own armor to him, but David was unable to use it. He reverted to that with which he was familiar and already skilled - his sling. Choosing “five smooth stones” from the brook, David went out against Goliath.
Much has been made of David’s five smooth stones. Some have explained them in a figurative sense as such things as faith, courage, righteousness, etc. I suppose that would make for a nice sermon. Others have suggested that there were other giants nearby (see 2 Samuel 21:18-22), and David was preparing himself should they show up. There is no indication in the text, however, that other giants besides Goliath stalked the ranks of this Philistine army.
Sometimes we try to go so deep into a text that we overlook the obvious. What is happening, and what is David doing? He is preparing for this fight with the weapon he knows best. David is a shepherd and has used his sling on countless occasions to protect his flock from predators. Why does he go to the brook? Because he knows that you find smooth stones in a stream and ones of the right size for slinging. Why are the stones smooth? Smooth stones will fly straighter and with greater velocity than those with ragged edges.
And now this question? Why five? If we didn’t already know the outcome of the contest, it would be easier for us to come up with this answer. He chose five because he had assessed the situation and knew that he might need more than one stone to bring down this giant! He was a huge man, a tough, seasoned warrior, and he had armor. David was just being practical as he prepared himself for this fight by insuring he had enough ammunition for the job!
So in addition to trusting in our God, we also need to be ready to do God’s will like David. Paul reminds his readers (Titus 3:1) “to be ready for every good work”. Pantries and pocketbooks, Bibles and baptistries, hearts and hands - be ready. Goliath is lurking nearby.