That's the background. Time and time again after quite short interludes the same abominations were displayed to God as if He didn't exist. We've got up to 1407 BC and sure enough, at the drop of a hat (or more probably the fluttering of an eyelid) The Israelites started whoring it up again after God had blessed them through an angel explaining to Balaam's donkey something he'd been unable to see for himself. It's true he did listen to the donkey when it explained the problem and did pronounce a blessing over Israel when he'd been paid to bleat curses. But the people moved in and clearly there were temple orgies, sacrifices to devils, unusual cocktails which aren't described but the ingredients are easy enough to imagine, trollops everywhere. God needed to be more emphatic!
Numbers 25:1-4 And Israel abode in Shittim, and the people began to commit whoredom with the daughters of Moab. And they called the people unto the sacrifices of their gods: and the people did eat, and bowed down to their gods. And Israel joined himself unto Baalpeor: and the anger of the LORD was kindled against Israel. And the LORD said unto Moses, Take all the heads of the people, and hang them up before the LORD against the sun, that the fierce anger of the LORD may be turned away from Israel.
As I say, it's unbelievable; even with the heads swinging there still dripping, one wretch decides it's a good time for wenching. Turns up with the latest hussy (you'd think she'd notice the heads and twig something was up!) bold as you like, straight into a tent for whatever hussies get up to in tents with plague evidently rampant again the vista really is most unappealing. Fortunately someone understood how much God loved this motley crew and followed them in, ran them through with a spear, thus averting even more plague than the 24,000 dead already plus however many supplied the heads.
1407 BC ——— Zimri and Cozbi ——— NUMBERS 25
Plague, incineration, chasms opening up to swallow whole families, strange fruit of heads hanging in the sun, more plague, orgies, idols, devils, and now Cozbi, who was a princess as well as a real bad floozy (I'm being polite) seems likely to evoke retribution from her people. What would God do?
Numbers 25:16-18 And the LORD spake unto Moses, saying, Vex the Midianites, and smite them: For they vex you with their wiles, wherewith they have beguiled you in the matter of Peor, and in the matter of Cozbi, the daughter of a prince of Midian, their sister, which was slain in the day of the plague for Peor's sake.
Over two decades in approximately the same area (about the size of Connecticut) whoredom had run rampant with the locals who must have found the land vacant AFTER it had been promised to someone else but moved in anyway. And when the legitimate owners arrived from Egypt, over those two decades they moved in on them too. The whole thing is absolutely disgusting and yet these are the women The Israelites spared? No wonder Moses ordered so many chopped up alive, even though from the age groups identified it's clear many of them wouldn't have been born when the abominations took place. God loves His people so much that the punishments are absolute and for many generations. I hope the timelines are useful. Here is a map helping to put everything in perspective.
Numbers 16:31-33, 34-35, 48-49
Numbers 21:23-25, 33-35
Numbers 25:6-9, 14-17
Numbers 31:17-20, 21-24, 32-35