God rejected the Moabites and the Ammonites (v. 38) with a holy and divine hatred, commanding His people not to “seek peace with them nor prosperity with them all your days forever” and forbidding an Ammonite or a Moabite to enter the congregation of Jehovah, “even to the tenth generation…forever” (Deut. 23:3-6; cf. Matt. 1:5 and note Matt. 1:53c).
Ishmael, brought forth by fleshly effort, was rejected by God (Gen. 21:10-12). Moab and Ben-ammi, brought forth by incest, were a shame in history. Only Isaac, brought forth by God’s grace, was used to fulfill God’s purpose.