Judges 3:2

2 and that afterward the sons of them should learn to fight with enemies, and to have custom of battle. (and so that through them their sons would learn to fight with their enemies, and know the ways of battle.)

Judges 3:2 Meaning and Commentary

Judges 3:2

Only that the generations of the children of Israel might know
and teach them war
That is, the following nations were left in the land, that the young generations of Israel might by their wars and conflicts with them learn the art of war, and be inured to martial discipline; which, if none had been left to engage with, they had been ignorant of: besides, their fathers in Joshua's time, as Jarchi and Kimchi observe, had no need to learn the art of war, for God fought for them; they did not get possession of the land by their own arm, and by their sword, but by the power of God in a miraculous way; but now this was not to be expected, and the Canaanites were left among them to expel, that they might be trained up in the knowledge of warlike affairs, and so be also capable of teaching their children the military art; which they should make use of in obeying the command of God, by driving out the remains of the Canaanites, and not give themselves up to sloth and indolence; though some think that the meaning is, that God left these nations among them, that they might know what war was, and the sad effects of it; and the difference of fighting with their enemies alone, as other men, and the Lord fighting along with them, and for them, as he did for their fathers:

at least such as before knew nothing thereof;
being either unborn, or at an age incapable of bearing arms, or learning the art of war.

Judges 3:2 In-Context

1 These be the folks which the Lord left alive, that in them he should teach Israel, and all men that knew not the battles of Canaanites; (These be the nations which the Lord left alive, so that through them he would teach the Israelites, all those who had not been part of the battles for Canaan;)

2 and that afterward the sons of them should learn to fight with enemies, and to have custom of battle. (and so that through them their sons would learn to fight with their enemies, and know the ways of battle.)

3 He left (alive the) five princes of the Philistines, and all Canaanites, and the people of Sidon, and Hivites that dwelled in the hill Lebanon, from the hill Baalhermon till to the entering of Hamath. (He left alive the five rulers of the Philistines, and all the Canaanites, and the people of Sidon, and the Hivites who lived on Mount Lebanon, from Mount Baalhermon unto Hamath Pass.)

4 And he left them, that in them he should assay Israel, (to see) whether they would hear the behests of the Lord, which he commanded to their fathers by the hand of Moses, either nay. (Yea, he left them alive, so that through them he could test Israel, to see whether they would listen to the Lord's commands, which he commanded to their fathers through Moses, or not.)

5 And so the sons of Israel dwelled in the midst of Canaanites, of Hittites, and of Amorites, and of Perizzites, and of Hivites, and of Jebusites, (And so the Israelites lived in the midst of the Canaanites, the Hittites, and the Amorites, and the Perizzites, and the Hivites, and the Jebusites,)