I Samuel 17:47 And all this assembly shall know that the LORD saveth not with sword and spear: for the battle is the LORD’s, and he will give you into our hands.
David has learned a truth that all of us must learn if we desire to be used of God. The Lord does not save with the sword and spear.
That is a blessing because the nation of Israel is standing there before the Philistines with very few swords and spears. Almost certainly the Philistines were mocking them. They had a giant. They had weapons.
The Israelites are standing their side of the valley with slings, sticks, and rocks plus no hero to fight for them. Possibly others saw what was lacking but David saw not the lack but the strength that he had that no Philistine had. He had the power of God. He knew that God could and would win the battle without earthly weapons or wisdom.
God gives those that He calls power to do His work plus the Living Word that works effectually in the lives of men and women. If God calls you to do battle for Him or if you will simply say “Here am I send me” you may go forth with faith and confidence.
The enemy may have more of some things than you do but the enemy lacks the one great ingredient to success. He has no personal intimate walk with the “Great I AM.”