Charles Ellicott Commentary Numbers 25:17

"Vex the Midianites, and smite them;" — Numbers 25:17 (ASV)

Vex the Midianites, and smite them. The Midianites appear to have been joint actors with the Moabites throughout all the opposition offered to Israel, and the chief actors in the wiles by which the Israelites were seduced. As descendants of Abraham, the father of the faithful, the Midianites should have feared and obeyed Abraham’s God, and shown brotherly kindness to God's people, who were their own relatives. The special judgments of God are directed against the sins of apostasy and seduction (Revelation 18:6).

Although the Moabites were not to be defeated with the Midianites , they nevertheless did not escape punishment but were excluded, even to the tenth generation, from the congregation of the Lord . Their exemption at this time from the judgment inflicted upon the Midianites was probably due not to their descent from Lot (for the Midianites were descended from Abraham), but to the fact that the measure of their sin was not yet full .