The sin of presumption

“When they returned to Joshua, they said, ‘Not all the people will have to go up against Ai. Send two or three thousand men to take it and do not weary all the people, for only a few men are there.’” Joshua 7:3
We notice many differences between the attacks on Jericho and Ai. Perhaps the foremost one is that God told them to attack Jericho, but at this point He had not yet told them to attack Ai (c.f. Josh. 7:2 with Josh. 8:1). Instead, Joshua had taken it upon himself to send spies to Ai, and he listened to their advice. These men came back, filled with self-confidence over the events of Jericho. Yet they had not really done anything to fight against Jericho – God had caused the walls to fall down and the people merely had to walk in and take plunder. They presumed the same thing would happen at Ai, that it too would be a cake walk.
In addition, there was sin in the camp. Achan had taken some of the things that God had order to be given over to Him by destroying them. The people were on a high, but God had not told them to move on just yet until that sin was dealt with. As a result, He allowed them to be defeated so they would humble themselves, fix the problem, and trust in Him as the source of their strength.
How often do we continue in our own strength after God does something amazing in our lives? Sometimes, like the children of Israel, God has to bring about a fall in our lives to get our attention regarding some sin we need to deal with. It’s a painful lesson, but a necessary one, to get rid of our self-confidence and make us recognise the true source of our strength.