History of Yom Kippur
The biblical account of Yom Kippur describes a day dedicated to atonement and abstinence. Leviticus 23:27 tells us that on the 10th day of the month of Tishrei, “You should do no work throughout that day. For it is a Day of Atonement ("Yom Kippurim") on which expiation is made on your behalf before the Lord your God. Indeed, any person who does not practice self-denial throughout that day shall be cut off from his people…”
In addition to the abnegation alluded to above, we are also told in Leviticus that on this day the High Priest would perform sacred rites in order to achieve expiation of the people’s sins. These rites included a lottery to choose two goats--one to be consecrated to God and one to "Azazel." While the exact meaning of the word Azazel is uncertain, the ritual required the High Priest to confess the sins of Israel on this Azazel-goat, and to set it free in the wilderness so that it “shall carry on it all their iniquities to an inaccessible region.” (Lev. 16:22) The goat consecrated to God was offered on the altar as a purification offering.
In rabbinic literature, Yom Kippur is given an additional name, Yom HaDin (Day of Judgement). This solemn day is the culmination of the aseret y’mei teshuvah (10 days of repentance) following Rosh Hashanah. To the rabbis, Rosh Hashanah marked the beginning of a spiritual trial for the souls of Israel, the 10 days of repentance could then be seen as a time for appeals, and Yom Kippur marked the climax--when the verdict was handed down. At this time God, the true judge, would decide the fate of all of Israel as individuals and as a community, and hopefully inscribe them into the Book of Life.
The rabbis follow through on the biblical theme of self-denial in their discussions of the daily pleasures from which one must abstain on Yom Kippur. Among them are eating, drinking, bathing and anointing oneself, wearing leather-soled shoes (at the time the most comfortable option), and abstaining from sexual relations. These limitations are debated at great length in the Talmudic tractate devoted to Yom Kippur, entitled Yoma (literally, "the Day").