The Torah states: An Ammonite or Moabite shall not enter the congregation of Hashem… because of the fact that they did not greet you with bread and water on the road when you were leaving Egypt (Devarim 25:4-5). Our Sages point out that the Jews actually did not even need bread and water, since for all those years that they were in the Wilderness the Manna descended for them from Heaven and they had water from Miriam’s Well. But the Torah is teaching correct behavior, that when guests arrive after traveling, it is correct to offer them food and drink. This is why the Ammonite and Moabite nations were punished and were forbidden to enter the congregation of Israel forever — even a tenth generation after converting. If so, we must learn a kal vachomer from this: If even these nations who refrained from extending charity to those who did not even need it were punished so severely, then a person who refrains from giving charity to those who truly do need it will all the more so be severely punished.
