In the previous verse, David tried wearing King Saul’s armor. It’s was too big. He had to approach Goliath with the familiar, his sling and a stone.
People will send you up against the giants in their life and yours, with their armor and the weapons of their warfare. It won’t work. You have to fight with what you’ve got in your sheperd’s bag. Five smooth stones.
Is there something in the bag that doesn’t belong? Someone else’s armor? Fear? Doubt? Unbelief? Insecurity? Shame? Sin?
Empty the bag! Go to the river…grab the Rock…Take down the giant.