19 and when thou comest nigh over against the children of Ammon, vex them not, nor contend with them; for I will not give thee of the land of the children of Ammon for a possession; because I have given it unto the children of Lot for a possession. 20 (That also is accounted a land of Rephaim: Rephaim dwelt therein aforetime; but the Ammonites call them Zamzummim, 21 a people great, and many, and tall, as the Anakim; but Jehovah destroyed them before them; and they succeeded them, and dwelt 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.