1 Samuel 17:40

“And he took his staff in his hand, etc.] His shepherd’s staff, which he used in keeping his father’s sheep, and chose rather to appear in the habit of a shepherd than of a soldier: and chose him five smooth stones out of the brook; which ran in the valley, which became smooth by lying in the water running over them; and which being smooth were fitter for his purpose, being the more easily cast out of the sling; though De Dieu is of opinion that these were parts or pieces of stones, cleft ones, which were rough and rugged, and which would more easily and firmly be fixed in the forehead of the Philistine: and put them in a shepherd’s bag which he had, even in a scrip; in which he had been wont…”

“brook--wady. bag--or scrip for containing his daily food. sling--The sling consisted of a double rope with a thong, probably of leather, to receive the stone. The slinger held a second stone in his left hand. David chose five stones, as a reserve, in case the first should fail. Shepherds in the East carry a sling and stones still, for the purpose of driving away, or killing, the enemies that prowl about the flock.”

“Staff - His shepherd's staff. These arms in themselves were contemptible, yet chosen by David; because he had no skill to use other arms; because he had inward assurance of the victory, even by these weapons; and because such a conquest would be more honourable to God, and most shameful, and discouraging to the Philistines. 1 Kings (1 Samuel) 17:41”

“17:40 A stream flowed through the valley of Elah (17:2). • A sling was a leather pouch attached to two leather thongs. When the sling containing a stone was whirled rapidly, one of the thongs could be released, sending the stone toward its target. David probably became deadly accurate with a sling as a shepherd, but the sling was used by warriors as well (Judg 20:16).”

“staff: Jdg 3:31, Jdg 7:16-20, Jdg 15:15, Jdg 15:16, Jdg 20:16; Co1 1:27-29 brook: or, valley bag: Heb. vessel, Mat 10:10 1 Kings (1 Samuel) 17:42”