the Disposition of the Spoils of War
This law, which subjected the victors to a whole week of separation and to special purification, instead of an immediate welcome into the camp, was intended to wean the Hebrews from the practice of war, giving them a higher standard than that of surrounding nations. Thus God educates us, by placing before us an ever higher standard, as we are able to obey it. It is easy to say hard things against this treatment of Midian, but extermination is sometimes the only way to safety.
For us the lesson is one of rigid separation. Some may be able to stand God’s searching fire; but others cannot bear that flame. Yet these may not go altogether free. See Num 31:23 . As strangers and pilgrims we must abstain from fleshly lusts. God demands our holiness, but discriminates in the method of producing it.