About three thousand men - The spies sent to reconnoitre the place (Joshua 7:3) reported that the town was meanly garrisoned, and that two or three thousand men would be sufficient to take it. These were accordingly sent up, and were repulsed by the Amorites.

So there went up thither of the people about three thousand men,.... Joshua detached from the army the largest number proposed, that there might be strength enough to take the place; and those he sent under proper officers to Ai, who went up to the very gate of the city, as appears from Joshua 7:5,
and they fled before the men of Ai; for upon their appearing at the gate of their city, they came out with all their forces against them, and as soon as they did, the children of Israel durst not face them, but without engaging with them fled at once: God having forsaken them, their courage failed, the dread of their enemies falling on them.

they fled before the men of Ai--An unexpected resistance, and the loss of thirty-six of their number diffused a panic, which ended in an ignominious rout.

They fled - Not having courage to strike a stroke, which was a plain evidence that God had forsaken then; and an useful instruction, to shew them what they were when God left them: and that it was God, not their own valour, that gave the Canaanites into their hands.