What does Joshua 7:13 mean?

Get up and make the people holy. Tell them, 'Get ready for tomorrow, because the Lord, Israel’s God, says: You have something forbidden among you, Israel. You won’t be able to stand against your enemies until you remove it.' Joshua 7:13 - Modern Text Bible

(Joshua is told to prepare the people for a process of purification. The community must deal with the hidden sin before they can move forward.)