Only unto the land of the children of Ammon thou camest not, nor unto any place of the river Jabbok, nor unto the cities in the mountains, nor unto whatsoever the LORD our God forbad us. Only unto the land of the children of Ammon thou camest not - God gave them their commission; and those only were to be cut off, the cup of whose iniquity was full. Though the Moabites and Ammonites were thus spared, they requited good with evil, for they fought against the Israelites, and cast them out of their possessions, Judges 11:4, Judges 11:5; 2 Chronicles 20:1, etc., and committed the most shocking cruelties; see Amos 1:13. Hence God enacted a law, that none of these people should enter into the congregation of the Lord even to their tenth generation: see Deuteronomy 23:3-6.
Commentary on the Bible, by Adam Clarke [1831].