Notes on the Bible, by Albert Barnes, [1834], at sacred-texts.com
The Midianites - The Moabites are not included. It would thus seem that it was the Midianites, and they only, who deliberately set themselves to work the corruption of Israel.
Avenge the Lord of Midian - The war against the Midianites was no ordinary war. It was indeed less a war than the execution of a divine sentence against a most guilty people.
Doubtless there were many among the Midianites who were personally guiltless as regards Israel. But the rulers deliberately adopted the counsel of Balaam against Israel, and their behests had been but too readily obeyed by their subjects. The sin therefore was national, and the retribution could be no less so.
But the commission of the Israelites in the text must not be conceived as a general license to slay. They had no discretion to kill or to spare. They were bidden to exterminate without mercy, and brought back to their task Num 31:14 when they showed signs of flinching from it. They had no alternarive in this and similar matters except to fulfill the commands of God; an awful but doubtless salutary manifestation, as was afterward the slaughter of the Canaanites, of God's wrath against sin; and a type of the future extermination of sin and sinners from His kingdom.
Were delivered - Or, "were told off."
Phinehas - He was marked out as the fitting director of the expedition by his conduct (compare Num 25:7-13) in the matter of Zimri and Cozbi.
With the holy instruments, and the trumpets - Or rather, "with the holy instruments, to wit, the trumpets," for the trumpets themselves seem to be the instruments intended.
And they slew ... were slain ... - Render: And the kings of Midian they put to death, beside those that fell in the battle; namely, etc. From which it would seem that beside these five, put to death after the battle, there were other Midianite kings who perished fighting. The five chieftains here mentioned were vassals of Sihon the Amorite Jos 13:21.
Goodly castles - Rather, both here and in Gen 25:16, hamlets. The word is derived from a word טוּר ṭûr,) signifying "a row" or "range" (compare Eze 46:23); and probably indicates those collections of rude dwellings, made of stones piled one on another and covered with tent-cloths, which are used by the Arabs to this day; and which are frequently mentioned as douars in narratives of the French campaigns in Algeria. These dwellings would be formed usually in a circle. See the word "Hazeroth," in Num 11:35.
The "prey" refers to the captives and live-stock: the "spoil" to the ornaments and other effects.
Caused ... to commit trespass - More literally, "became to the children of Israel for a cause (or, incitement) of treachery to the Lord."
Brass - Render copper. See Gen 4:22 note. The verse is curious as illustrating the variety of metals in use at this early date for domestic purposes. All these metals were common in Egypt centuries before the date of the Exodus.
An heave-offering - Render simply an offering, and compare Num 18:24. The verb from which the word here rendered "heave-offering" is derived, is rightly translated "levy" in Num 31:28.
Compare Num 31:11, and render "And the prey" (i. e., the live prey) "in addition to the spoil which the men of war seized, etc." The "spoil" is described in Num 31:50.
The number of sheep, beeves, asses, and persons taken is given in this and following verses in round thousands. Hence, the Lord's tribute (Num 31:29, Num 31:37-38, etc.), being the 500th part of the half, comes out also in round numbers. The enormous amount both of live stock and of personal ornament was characteristic of the Midianites. When they invaded Israel in the days of the Judges, their wealth was still of the same kind (Jdg 6:5; Jdg 8:24 ff). The Bedouins, notwithstanding their wild nomadic life, retain their ancestral love of finery to the present day.
There is no mention of any resistance on the part of the Midianites. The Israelites saw in this and in the preservation of all those engaged, proofs that the Lord had been with them in the work, and hence, the free-will oblation of Num 31:50.
The "chains" were "armlets" Sa2 1:10. The "rings" were "finger-rings," or "seal-rings;" and the "tablets" were worn suspended from the neck Exo 35:22.
To make an atonement for our souls before the Lord - Compare Exo 30:11-16. The atonement was not for any special offence committed (which would have called for a sacrifice of blood-shedding), but rather like the half-shekel given at the census in the Book of Exodus (loc. cite), was an acknowledgment of having received undeserved mercies. These, if unacknowledged, would have entailed guilt on the soul.
The value of the offering was about 20,000 British pounds.
This verse seems to imply that the soldiers, as distinct from the officers (compare Num 31:49), did not make any offering from their plunder. Of course besides the gold there would be much spoil of less precious materials; see Num 31:20, Num 31:22.