What does Judges 3:2 mean?
The Lord said He would leave specific nations to exist in and around Israel. The presence of these wicked cultures would "test" the Israelites to see if they will be faithful to Him. As God is all-knowing, this testing is more of a "demonstration," proving that which the Lord already sees. He warned the people of Israel not to let the depraved Canaanite culture survive (Deuteronomy 20:16–18). When the people disobeyed, God chose to use their own sin as a source of punishment. God will use these nations to attack and harm Israel to see if they will begin to obey Him once more.The purpose, then, is to "teach war" to new generations of Israelites who have not had to rely on God during war as the previous generations did. In this context, the writer does not mean teaching strategies of attack and defense, or the methods of subduing an enemy. God literally means to teach the Israelites to trust Him, to obey Him, and to rely on Him, as they experience what it means to be at war.