"And David said, 'The LORD who delivered me from the paw of the lion and from the paw of the bear will deliver me from the hand of this Philistine.' And Saul said to David, 'Go, and the LORD be with you!' 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 17:37-40 ESV
Saul meant well. He offered David the weapons he would have used if he had gone himself. David was smart enough not to take them.
"And the Philistine moved forward and came near to David, with his shield-bearer in front of him. And when the Philistine looked and saw David, he disdained him, for he was but a youth, ruddy and handsome in appearance... When the Philistine arose and came and drew near to meet David, David ran quickly toward the battle line to meet the Philistine. And David put his hand in his bag and took out a stone and slung it and struck the Philistine on his forehead. The stone sank into his forehead, and he fell on his face to the ground. So David prevailed over the Philistine with a sling and with a stone, and struck the Philistine and killed him. There was no sword in the hand of David. Then David ran and stood over the Philistine and took his sword and drew it out of its sheath and killed him and cut off his head with it. When the Philistines saw that their champion was dead, they fled." - 1 Samuel 17:41-42, 48-51 ESV
Those smooth stones are tried. Water has washed over them. Grace is the thinking that has conquered us and we have used it before in our lives. Prayer is proven. The Bible is proven. God's thinking will immobilize the giant. Then we can use his sword to cut his head off.
People mean well when they offer us their carnal weaponry but in the life or death situation there is nothing like those smooth stones. There is nothing like prayer. There is nothing like reading the Bible and seeing the examples given to us there and gleaning from them. There is nothing like grace, forgiveness and love.
If someone must die let it be with the sword they took to battle and not one we took into it. The staff and sling were weapons used to protect the flock. Those are the ones we want.