Achan’s Sin: Hidden Covetousness and the Valley of Trouble. Sometimes the greatest danger to God’s people is not the enemy outside, but the compromise inside. After the stunning victory at Jericho, Israel expected to keep marching forward in triumph. Instead, they stumbled in humiliating defeat at Ai because of one man’s hidden sin. The story of Achan shows the seriousness of sin, the holiness of God, and the need for atonement—a theme that finds its fulfillment in Christ.