Fight together

"The Philistines gathered for battle in Socoh, a town in Judah; they camped at a place called Ephes Dammim, between Socoh and Azekah. Saul and the Israelites assembled and camped in the Valley of Elah, where they got ready to fight the Philistines. The Philistines lined up on one hill and the Israelites on another, with a valley between them. ...

Goliath stood and shouted at the Israelites, “What are you doing there, lined up for battle? I am a Philistine, you slaves of Saul! Choose one of your men to fight me. If he wins and kills me, we will be your slaves; but if I win and kill him, you will be our slaves. Here and now I challenge the Israelite army. I dare you to pick someone to fight me!” When Saul and his men heard this, they were terrified."

~ 1 Samuel 17.1-11 GNB

Saul had a military strategy to face the Philistine army, but he did not stick to it. Someone in the Philistine army thought Saul's strategy was sound and they got creative to find a way to win the war quicker. So they sent Goliath.

When Goliath issued an individual challenge to bypass a battle involving the entire army, Saul mistakenly took up to it. They were at war and there was nothing that could make Saul agree to the challenge. He could just order the entire army to attack the Philistine army. But Saul focused on the wrong thing.

Individually, there was nobody among the Israelites who could match Goliath. It seemed humanly impossible to win a fight with Goliath. But they were supposed to fight together as one army under the LORD, not individually.

They were called to fight together and they forgot that.