On the Day of Atonement it is forbidden to eat, drink, bathe, put on any sort of oil, put on a sandal, or engage in sexual relations.The Torah portion is not as explicit as the Midrash in its list of prohibitions:
In the seventh month, on the tenth day of the month, you shall practice self-denial; and you shall do no manner of work, neither the citizen nor the alien who resides among you. For on this day atonement shall be made for you to cleanse you of all your sins; you shall be clean before the Lord. It shall be a sabbath of complete rest for you, and you shall practice self-denial; it is a law for all time.(Other relevant verses)
Since the midrash prohibitions are so extensive, the Rabbi asks, in what other situation is eating, drinking, bathing, anointing, and wearing leather on the feet prohibited? Answer: The frequently persecuted Jewish communities of medieval Europe used the threat of a limited form of excommunication, called niddui, to keep their members in line. The niddui was announced by the blowing of the shofar, after which the community members weren’t supposed to come within ~6’ of the offender or eat with him, and the offender was not supposed to cut his hair, wear shoes, etc. So on Yom Kippur, we are essentially placing ourselves in niddui for the day due to our sins over the year, and that’s why we blow the shofar, don’t eat, don’t bathe, and don’t wear leather shoes.
As a business student the concept of niddui is interesting also for its implications in emerging markets. For class we read this article “Private Order under Dysfunctional Public Order” from the Michigan Law Review (Recommended read. Most of the article is available online.), in which the authors demonstrate how in emerging markets that do not have strong institutions to support small businesses, such as a functioning court of law or credit bureaus, entrepreneurs still manage to flourish by creating extra-legal systems of their own. For example, in the ethnic Chinese community in Vietnam if one business cheated another business then the entire community would boycott the cheater. By looking at these communities which have created niddui of their own, we can perhaps better understand the context in which the concept evolved in the Jewish tradition, and what life may have been like in a Jewish village in medieval Europe.