Moses is told that before he dies, the last thing he must do is to destroy Midian because they nearly succeeded in corrupting almost the whole of the Israelite leadership below Moses and Aaron. Notice the Torah mentions Midian and not Moab but in fact they were partners from the start. The Midrash suggests that they merged.
So, off the Israelites go, form an army and Phineas joins them. In the general slaughter, they kill Balaam Ben Beor the magician who we last heard of returning home after his failed attempt to curse. Now it seemed he could not stay away. Having failed once he wanted to try again. So much for his protesting that he was a servant of God and wanted to obey Him. This why the Midrash says, although the Torah is not explicit, that it was Balaam’s advice to send in the women. Here it simply says that he instigated the worship of Baal Peor which we know involved temple prostitution and religious orgies. Is it an accident that Balaam’s father is Beor and the pagan worship is Peor?
Following the conquest Moses insists that the captured vessels be purified if the Israelites want to use them. This is the origin of the laws of koshering vessels as well as dipping them into a Mikvah when they are bought for kosher use.” Any vessel that is used on or under conditions of heat (fire) can only be purified by fire. Otherwise it can be purified by water.
Symbolically the objects are now to be used under conditions of holiness, spirituality. Like humans entering into a new state, so objects can transition from one kind of usage into another.