Yom Kippur
Purification

In Leviticus 16:30, the Torah summarizes the purpose of Yom Kippur as follows:

For on this day atonement shall be made for you, to purify you; from all your sins before the Lord you shall be purified.

There are two forms of impurity in Judaism (see Tumah and taharah): ritual impurity (e.g. when one touches a corpse) and moral impurity (when one commits a serious sin). While the Yom Kippur Temple service did purify the Temple if it had become ritually impure, the emphasis of the day is on the Jewish people's purification from moral impurity.

Leviticus 16:30 mentions purification twice. According to Netziv, the first mention is a promise that God will purify Israel on this day, while the second is a command, calling on Israel to purify themselves through repentance. Thus, on this day Jews do their utmost to repent. But if, by the end of the day, they have reached the limits of their ability and are still morally flawed, God extends them forgiveness and purification anyway.

Jeremiah 17:13 states that "Israel's hope (mikveh) is in God". According to Rabbi Akiva, this verse alludes to a ritual purification bath (also pronounced mikveh), and thus on Yom Kippur God metaphorically becomes a mikveh in which Israel immerses and purifies itself. This idea is symbolized by immersion in an actual mikveh. In the Yom Kippur Temple service, the High Priest would immerse upon putting on and taking off his white Yom Kippur garments; the rabbis counted no fewer than five immersions over the course of the day's service. Among modern-day Jews, too, there is a custom of immersion before Yom Kippur (though not on Yom Kippur itself, as bathing is forbidden in normal circumstances).

When the scapegoat was selected on Yom Kippur to symbolically carry the people's sins to the desert, a crimson cord was tied around its horns. While the practical purpose of this cord was to distinguish the scapegoat from the goat which was to be slaughtered, it also symbolized the sin which the scapegoat was carrying away. Isaiah 1:18 promises that if the Jewish people repents, "if sins are like crimson, they shall become white as snow." According to tradition, in some years the scapegoat's cord would miraculously turn white to indicate that the people's sins were forgiven and purification achieved in that year.
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