Joshua 7:2,3

Go up and view the country They were not to go into the city of Ai, but into the country belonging to it, that they might understand the state of the place and people. Let two or three thousand go up and smite Ai There was no little self-confidence and presumption in this counsel: Ai, it appears, was strong by its situation, and guarded by twelve thousand men; so that there was no probability of taking it with two or three thousand. God, however, wisely permitted this advice to be followed, that Achan's sin might be brought to light and punished, and the people in general, who were evidently lifted up through their late success, might be awakened, humbled, and reformed, and that with as little mischief and reproach as might be. For if the defeat of these few caused such consternation in Joshua and the elders, and probably in all the host, it is easy to guess what dread it would have caused if the whole army had been defeated.