Complete Commentary on the Whole Bible, by Matthew Henry, at sacred-texts.com
(Num 31:1-6) War with Midian.
(Num 31:7-12) Balaam slain.
(Num 31:13-18) Those slain who caused sin.
(Num 31:19-24) Purification of the Israelites.
(v. 25-47) Division of the spoil.
(Num 31:48-54) Offerings.
All who, without commission from God, dare to execute private revenge, and who, from ambition, covetousness, or resentment, wage war and desolate kingdoms, must one day answer for it. But if God, instead of sending an earthquake, a pestilence, or a famine, be pleased to authorize and command any people to avenge his cause, such a commission surely is just and right. The Israelites could show such a commission, though no persons now can do so. Their wars were begun and carried on expressly by Divine direction, and they were enabled to conquer by miracles. Unless it can be proved that the wicked Canaanites did not deserve their doom, objectors only prove their dislike to God, and their love to his enemies. Man makes light of the evil of sin, but God abhors it. This explains the terrible executions of the nations which had filled the measure of their sins.
The Israelites slew the Kings of Midian. They slew Balaam. God's overruling providence brought him thither, and their just vengeance found him. Had he himself rightly believed what he had said of the happy state of Israel, he would not have thus herded with the enemies of Israel. The Midianites' wicked wiles were Balaam's projects: it was just that he should perish with them, Hos 4:5. They took the women and children captives. They burnt their cities and castles, and returned to the camp.
The sword of war should spare women and children; but the sword of justice should know no distinction, but that of guilty or not guilty. This war was the execution of a righteous sentence upon a guilty nation, in which the women were the worst criminals. The female children were spared, who, being brought up among the Israelites, would not tempt them to idolatry. The whole history shows the hatefulness of sin, and the guilt of tempting others; it teaches us to avoid all occasions of evil, and to give no quarter to inward lusts. The women and children were not kept for sinful purposes, but for slaves, a custom every where practised in former times, as to captives. In the course of providence, when famine and plagues visit a nation for sin, children suffer in the common calamity. In this case parents are punished in their children; and for children dying before actual sin, full provision is made as to their eternal happiness, by the mercy of God in Christ.
The Israelites had to purify themselves according to the law, and to abide without the camp seven days, though they had not contracted any moral guilt, the war being just and lawful, and commanded by God. Thus God would preserve in their minds a dread and detestation of shedding blood. The spoil had been used by Midianites, and being now come into the possession of Israelites, it was fit that it should be purified.
Whatever we have, God justly claims a part. Out of the people's share God required one in fifty, but out of the soldiers' share only one in five hundred. The less opportunity we have of honouring God with personal services, the more should we give in money or value.
The success of the Israelites had been very remarkable, so small a company overcoming such multitudes, but it was still more wonderful that not one was slain or missing. They presented the gold they found among the spoils, as an offering to the Lord. Thus they confessed, that instead of claiming a reward for their service, they needed forgiveness of much that had been amiss, and desired to be thankful for the preservation of their lives, which might justly have been taken away.