What does 1 Samuel 17:21 mean?
The Philistines are camped across a valley from Israel (1 Samuel 17:1–3). Through Goliath, the Philistines have proposed champion warfare: one man from each side would serve as a representative in a duel. The survivor's people would be the victors, and the other nation would become their servants (1 Samuel 17:8–10). The Philistine champion, enormous and heavily armored, taunts the Israelites for forty days (1 Samuel 17:16). Even so, each morning the troops gather and line up for war. Battles during this time often began in an orderly fashion, with two armies forming long lines within full view of the enemy, who did the same. In this way, they could easily assess each other's strengths and weakness and adjust before attacking or defending.David's three eldest brothers are with the Israelite camp. Jesse, David's father, has sent his youngest son with food for his brothers and their division (1 Samuel 17:17–18). Samuel anointed David to serve as Israel's next king (1 Samuel 16:1–13), though he may not yet be fully aware of the specific reason for the anointing. It would be at least ten years before David assumed the political throne, but the Spirit of the Lord is clearly with him. God has also provided a means by which David is exposed to the duties of kingship through his service to King Saul (1 Samuel 16:14–23). David is apparently too young to be part of the Israelite army; he remains his family's shepherd in addition to serving at Saul's palace as armor-bearer and musician (1 Samuel 17:15).
On this day, David arrives at the Israelite military camp just as his brothers and the army are forming their battle line, shouting war cries. War cries were meant to be aggressive. They would serve to intimidate the enemy and encourage the troops. The war cries should show the Israelites' courage and readiness for the battle. That posture of courage will quickly vanish when the Philistine champion Goliath steps into the space between the two armies to make his daily challenge to any man who would fight him (1 Samuel 7:4–11).