Then Saul clothed David with his armor. He put a helmet of bronze on his head and clothed him with a coat of mail, and David strapped his sword over his armor. And he tried in vain to go, for he had not tested them. Then David said to Saul, “I cannot go with these, for I have not tested them.” So David put them off. Then he took his staff in his hand and chose five smooth stones from the brook and put them in his shepherd’s pouch. His sling was in his hand, and he approached the Philistine. -1 Samuel 17:38-40
Then David said to Ahimelech, “Then have you not here a spear or a sword at hand? For I have brought neither my sword nor my weapons with me, because the king’s business required haste.” 9 And the priest said, “The sword of Goliath the Philistine, whom you struck down in the Valley of Elah, behold, it is here wrapped in a cloth behind the ephod. If you will take that, take it, for there is none but that here.” And David said, “There is none like that; give it to me.” -1 Samuel 21:8-9
Within the story of David, this particular pair of verses tell a story all of themselves. Here is David, unafraid, but unable to use the armor of Saul, confronting Goliath. In using the word “test,” in relation to Saul’s armor, David is saying he doesn’t know if he can trust the armor against Saul’s strength. He hasn’t examined the armor for weakness or defect, nor tried it in battle against a lesser foe. He prefers his own sling and smooth stones over the armor of a king.
And yet, when David is fleeing from that same king just a few years later, does he trust in his sling and stones? No, he takes the sword of Goliath. David, in other words, fights with the sword of a man too large and fearful for Saul, the king — and anyone else in Israel — to overcome.
Two things should jump out at us.
First, the symbolism to the Philistines at Gath, when he later comes there, cannot be missed. Here is David, the man who killed the champion of Gath, a champion no-one believed could be defeated in single combat, coming to the city where that champion lived. And with him he carries the sword of the defeated champion itself.
Second, David’s growth is such that he has moved from being unable to support Saul’s armor to being able to use the sword of a man who defeated Saul. He has leapfrogged Saul in his abilities and strength. But we shouldn’t limit this growth to the physical, for there is clearly a spiritual side to it as well. David has moved from the more primitive weapon to the more advanced one. He does not have less faith (no-one says to David, “Why do you need a sword? Don’t you trust God?”), but more. But even with more faith, he still realizes he needs the appropriate tools. This is not single combat, but general warfare; a sling is not the proper tool to have in hand.