What is the message for us in this passage?
The easy meaning — if you have a sin in your life, God will allow you to be defeated — is not what this passage says. This is not a call to personal confession.
This passage is about corporate responsibility — the actions of one member is the action of the whole body. One man sins, so the whole people has sinned. God holds all Israel accountable for the actions of one man.
As modern people, we often find the idea of corporate responsibility difficult to accept. We prefer individual responsibility. We certainly don’t want to be treated badly because of what someone else does or doesn’t do.
But corporate responsibility has one very large upside.
In the New Testament, we still have corporate responsibility, but God has performed a wonderful reversal — one man’s holiness brings holiness to the whole people. In this passage, Achan’s sin separating Israel from God, but in the New Testament, Jesus’ holiness brought the whole Church into God’s presence. Israel was received punishment for Achan’s sin; the Church receives blessings for Christ’s obedience.
God still deals with the Church as a corporate body. But, thanks to Jesus, those dealings are wonderful. I am blessed — not because I obey — but because Jesus did.