19 and when you approach the frontier of the sons of Ammon, do not harass them or contend with them, for I will not give you any of the land of the sons of Ammon as a possession, because I have given it to the sons of Lot for a possession.' 20 (That also is known as a land of Reph'aim; Reph'aim formerly lived there, but the Ammonites call them Zamzum'mim, 21 a people great and many, and tall as the Anakim; but the Lord destroyed them before them; and they dispossessed them, and settled in their stead;
Matthew Henry's Commentary on Deuteronomy 2:19-21
Commentary on Deuteronomy 2:8-23
(Read Deuteronomy 2:8-23)
We have the origin of the Moabites, Edomites, and Ammonites. Moses also gives an instance older than any of these; the Caphtorims drove the Avims out of their country. These revolutions show what uncertain things wordly possessions are. It was so of old, and ever will be so. Families decline, and from them estates are transferred to families that increase; so little continuance is there in these things. This is recorded to encourage the children of Israel. If the providence of God has done this for Moabites and Ammonites, much more would his promise do it for Israel, his peculiar people. Cautions are given not to meddle with Moabites and Ammonites. Even wicked men must not be wronged. God gives and preserves outward blessings to wicked men; these are not the best things, he has better in store for his own children.