Jewish Mysticism
On account of his mercy and lovingkindness the Lord, blessed be he, instituted for Israel one day during the year to purify them from their impurities and to cleanse them, and he called it yom ha-kippurim. The reason it is called yom ha-kippurim in the plural is because these two emanations are united on that very day, the emanation of Binah and the emanation of Malkhut. Thus, the emanation of Binah purifies and cleanses every kind of filth and dirt that Israel bestowed on the emanation of Malkhut. When these two emanations are united to reverse [the judgments] to the merits of Israel and to purify their dirt, they are called accordingly yom ha-kippurim. Thus I will provide an allusion- “If your sins are like crimson, they will be whitened like snow” (Isa. 1-18). The supernal one is called Lebanon, and the lower one is garbed in a garment of crimson. Israel must transform the crimson garment into white, and therefore it is called yom ha-kippurim. . . . Since these two emanations, which correspond to one another in the secret of the supernal mother and the lower mother, are involved on this day in the purification of Israel, sexual intercourse is prohibited on Yom Kippur, even though it is permissible on Sabbaths and Festivals. The secret is known to those who know the esoteric lore. “And besides, she is in truth my sister, my father’s daughter though not my mother’s daughter; and she became my wife” (Gen. 20-12). This is the secret of its being called yom ha-kippurim. Understand this well.

Translated by Elliot Wolfson in “Fore/giveness on the Way- Nesting in the Womb of Response,” Graven Images- Studies in Culture, Law, and the Sacred 4 (1998)- 153-169.