That - Israel might know, to teach them war - This was another reason why the Canaanites were left in the land, that the Israelites might not forget military discipline, but habituate themselves to the use of arms, that they might always be able to defend themselves against their foes. Had they been faithful to God, they would have had no need of learning the art of war; but now arms became a sort of necessary substitute for that spiritual strength which had departed from them. Thus Gods in his judgments leaves one iniquitous nation to harass and torment another. Were all to turn to God, men need learn war no more.

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.

Only that the generations of the children of Israel might know, to teach them war, at the least such as before knew {b} nothing thereof;

(b) For they trusted in God and he fought for them.

3:2 Teach them war - That by the neighbourhood of such warlike enemies, they might be purged from sloth and security, and obliged them to innure themselves to martial exercises, and to stand continually upon their guard, and consequently to keep close to that God whose assistance they had so great and constant need of.

3:1-7 As the Israelites were a type of the church on earth, they were not to be idle and slothful. The Lord was pleased to try them by the remains of the devoted nations they spared. Temptations and trials detect the wickedness of the hearts of sinners; and strengthen he graces of believers in their daily conflict with Satan, sin, and this evil world. They must live in this world, but they are not of it, and are forbidden to conform to it. This marks the difference between the followers of Christ and mere professors. The friendship of the world is more fatal than its enmity; the latter can only kill the body, but the former murders many precious souls.