§ 02 · King James Bible
Judges 3:1
Now these are the nations which the LORD left, to prove Israel by them, even as many of Israel as had not known all the wars of Canaan;
Simple English
Now, these are the nations that the Lord didn't eliminate. He did this to test Israel using them. It was for the benefit of those Israelites who hadn't experienced all the wars in Canaan.
* Work in progress - there may be occasional inaccuracies