Now these are the nations which Yahweh left, to prove Israel by them, even as many [of Israel] as had not known all the wars of Canaan;
"The nations Jehovah left ... to prove Israel"  (Judges 3:1).  This passage gives two reasons why the Lord did not drive out all of the Canaanites before Israel, namely: (1) to prove them, whether or not they would obey the Lord; and (2) to teach those ignorant of it, the art of war; (3) A third reason is also given, namely, that of punishing Israel for their disobedience.