At Jericho the Israelites knew they needed God's supernatural power to bring down the walls but at Ai they thought a small army would suffice. However they suffered a massive defeat. Not only were they under manned but they were also unaware of the sin Achan had committed. When Joshua ultimately conquered Ai he took the whole army with him as God directed (8:1).
When we experience a victory in our Christian life it is easy to think that it was due, in some part, to our own competence. Even in capturing Jericho the Israelites may have appreciated God's intervention but still took some credit for taking the city. They did not realize how truly dependant on God they were until they were crushed at Ai.
When we are called to lead worship, teach a Bible study group, preach a sermon, write a devotional article or any God directed task even if we have done it a hundred times before, we would do well to acknowledge our dependency on God. Our familiarity with a task should not assume competency.
Sometimes God allows disappointment and disillusionment to humble us so we will acknowledge our inadequacy and accept his help. It is not easy to do in a world that values self-sufficiency. We go against the wisdom of the world when we chose to rely on God's grace rather than our own abilities.
After a spiritual victory are we like Paul who said: "We have done so, relying not on worldly wisdom but on God’s grace" (2 Corinthians 1:12)?