12 Moreover, the Horim had formerly inhabited Seir, but the descendants of Esau dispossessed them, destroying them and settling in their place, as Israel has done in the land that the Lord gave them as a possession.) 13 "Now then, proceed to cross over the Wadi Zered." So we crossed over the Wadi Zered. 14 And the length of time we had traveled from Kadesh-barnea until we crossed the Wadi Zered was thirty-eight years, until the entire generation of warriors had perished from the camp, as the Lord had sworn concerning them. 15 Indeed, the Lord's own hand was against them, to root them out from the camp, until all had perished. 16 Just as soon as all the warriors had died off from among the people, 17 the Lord spoke to me, saying, 18 "Today you are going to cross the boundary of Moab at Ar. 19 When you approach the frontier of the Ammonites, do not harass them or engage them in battle, for I will not give the land of the Ammonites to you as a possession, because I have given it to the descendants of Lot." 20 (It also is usually reckoned as a land of Rephaim. Rephaim formerly inhabited it, though the Ammonites call them Zamzummim, 21 a strong and numerous people, as tall as the Anakim. But the Lord destroyed them from before the Ammonites so that they could dispossess them and settle in their place. 22 He did the same for the descendants of Esau, who live in Seir, by destroying the Horim before them so that they could dispossess them and settle in their place even to this day.
Matthew Henry's Commentary on Deuteronomy 2:12-22
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.