Rahab agreed to the three conditions, and after the Israelites left she tied the cord to the window. According to verse 18 the Israelite spies instructed Rahab to tie the red cord to her window when we invade your land. But the present verse states When they had gone, she tied the red cord to the window. The problem may be resolved by leaving implicit When we invade your land of verse 18. It is also legitimate to render verse 18 “When we invade your land, be sure this red cord is tied to the window.”

Quoted with permission from Bratcher, Robert G. and Newman, Barclay M. A Handbook on Joshua. (UBS Helps for Translators). New York: UBS, 1983. For this and other handbooks for translators see here .