1 Chapter 25 tells of Israel’s sins on the steppes of Moab, and God’s punishment. In the overall plan of the book, here we have another possible threat to God’s program, although here it comes from within the camp (Balaam was the threat from without). If the Moabites could not defeat them one way, they would try another. The chapter has three parts: fornication (vv. 1–3), God’s punishment (vv. 4–9), and aftermath (vv. 10–18). See further G. E. Mendenhall, The Tenth Generation, 105–21; and S. C. Reif, “What Enraged Phinehas? A Study of Numbers 25:8,” 90 (1971): 200–206.
2 This first preterite is subordinated to the next as a temporal clause; it is not giving a parallel action, but the setting for the event.
3 The account apparently means that the men were having sex with the Moabite women. Why the men submitted to such a temptation at this point is hard to say. It may be that as military heroes the men took liberties with the women of occupied territories.

In other versions

While Israel lived in Shittim, the people began to whore with the daughters of Moab.

While Israel was staying in Shittim, the men began to indulge in sexual immorality with Moabite women,

While Israel was staying in the Acacia Grove, the people began to prostitute themselves with the women of Moab.

While the Israelites were camped at Acacia Grove, some of the men defiled themselves by having sexual relations with local Moabite women.

When Israel dwelled in Shittim, the people began to prostitute themselves with the daughters of Moab.

And Israel abode in Shittim, and the people began to commit whoredom with the daughters of Moab.

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