An Ammonite or Moabite can't enter the congregation of the Lord for ten generations. Why is that?


Because they hired Balaam to curse God.

An Ammonite or Moabite shall not enter into the congregation of the LORD; even to their tenth generation shall they not enter into the congregation of the LORD for ever:

Because they met you not with bread and with water in the way, when ye came forth out of Egypt; and because they hired against thee Balaam the son of Beor of Pethor of Mesopotamia, to curse thee. Deuteronomy 23:3-4