19 and come near over against the children of Ammon; thou shalt not distress them nor attack them; for I will not give thee of the land of the children of Ammon a possession; for unto the children of Lot have I given it as a possession. 20 (That also is reckoned a land of giants: giants dwelt therein in time past, and the Ammonites call them Zamzummim; 21 a people great, and many, and tall as the Anakim; and Jehovah destroyed them before them, and they dispossessed 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.