Numbers 31:1

“And the Lord spake unto Moses, etc.] After the plague upon Israel for their fornication and idolatry, into which they were drawn by the daughters of Moab and Midian, and after the sum of the people was taken in the plains of Moab, and various laws given or repeated, and a little before the death of Moses: saying; as follows.”

“THE MIDIANITES SPOILED AND BALAAM SLAIN. (Num. 31:1-54) the Lord spake unto Moses, Avenge the children of Israel of the Midianites--a semi-nomad people, descended from Abraham and Keturah, occupying a tract of country east and southeast of Moab, which lay on the eastern coast of the Dead Sea. They seem to have been the principal instigators of the infamous scheme of seduction, planned to entrap the Israelites into the double crime of idolatry and licentiousness [Num 25:1-3, Num 25:17-18] by which, it was hoped, the Lord would withdraw from that people the benefit of His protection and favor. Moreover, the Midianites had rendered themselves particularly obnoxious by entering into a hostile…”

“31:1-2 The Lord ordered Moses to lead Israel in a war of retaliation against the Midianites, who had joined the Moabites in leading the Hebrews into idolatry (ch 25). The Midianites were a tribal people who inhabited the arid and semiarid regions south and east of Palestine and east of the Jordan River; they were counted among the “people of the east” (Judg 6:3, 33; 7:12). They lived in camps or settlements and were famous for their knowledge of desert transportation (cp. Gen 37:28, 36; Isa 60:6). While they were descended from Abraham (Gen 25:1-2) and had been friendly toward Moses (Exod 2:15–3:1; cp. Num 10:29), the elders of Midian had joined Balak in hiring Balaam to curse Israel (22:4,…”

“The Campaign. - After the people of Israel had been mustered as the army of Jehovah, and their future relation to the Lord had been firmly established by the order of sacrifice that was given to them immediately afterwards, the Lord commanded Moses to carry out that hostility to the Midianites which had already been commanded in Num 25:16-18. Moses was to revenge (i.e., to execute) the revenge of the children of Israel upon the Midianites, and then to be gathered to his people, i.e., to die, as had already been revealed to him ( Num 27:13). "The revenge of the children of Israel" was revenge for the wickedness which the tribes of the Midianites who dwelt on the east of Moab (see at Num 22:4)…”