Synopsis of the Books of the Bible, by John Nelson Darby, [1857-62], at sacred-texts.com
Numbers Chapter 31
War is found in the wilderness (though it is not characteristic of it) whenever we fall into the snares the enemy there lays for us. There are always conflicts in the heavenly places in order to the enjoyment of the things promised there. But in the wilderness it is patience which is in exercise. But if there be failure, if we fall into idolatry, if we commit fornication with the world by yielding to its baits, if in any way whatever we contract friendship with the world in the desert, we make wars for ourselves, without having even the advantage of acquiring, in this kind of warfare, any spiritual ground. God is obliged to make our relations with the world undergo a total change. If we had not formed intimacies with them, we should not have had that trouble; but, since as our friends they deceive us, we must become enemies. Having no relations whatever with them is our proper and peaceful position.
How often we must act the part of enemies with the world, because we have sought to have to do with them as friends, and they were a snare to our souls! However, God gives a complete victory as soon as we treat them as foes: only, all that seduced must be utterly destroyed. There must be nothing spared, no concession.
The Lord orders also concerning the joy resulting from the wars of His people with their enemies. He chooses whom He will for the war, and honours them; but He will also honour, in their place, those who have been left behind according to His sovereign will, and who have faithfully discharged the perhaps less arduous task allotted to them; but who have, however, done it according to His will. God Himself is also recognised there in the Levites and the priests.