The words, “said I,” are not in the Hebrew. The words “rise up, and get you over the brook Zered” (Numbers 21:12 note) connect themselves with Deuteronomy 2:9, and form the conclusion of what God said to Moses.
Matthew Henry
Concise Bible Commentary
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.
SDA Bible Commentary (limited)
Volume 1-7
13. The brook Zered. Compare Num. 21:12. The modern Wâdi el-Hesa, at the southeastern corner of the Dead Sea.