This law forbids only the naturalization of those against whom it is directed. It does not forbid their dwelling in the land; and seems to refer rather to the nations than to individuals. It was not understood at any rate to interdict marriage with a Moabitess; compare Ruth 1:4; Ruth 4:13. Ruth however, and her sister were doubtless proselytes.
Compare the marginal reference. The Moabites and the Ammonites are to be regarded as clans of the same stock rather than as two independent nations, and as acting together. Compare 2 Chronicles 20:1.