So he tries to give the shepherd his armor, and the shepherd says, "" No. "" He says, "" I can't wear this stuff. "" The Biblical verse is, "" I cannot wear this for I have not proved it, "" meaning, "" I've never worn armor before. You've got to be crazy. "" So he reaches down instead on the ground and picks up five stones and puts them in his shepherd's bag and starts to walk down the mountainside to meet the giant.