Chasidut zu Wajikra 16:30

As we learned in Lesson Twelve, Yom Kippur is the day of yechidah. The author of the Tanya found a hint to yechidah in the verse about Yom Kippur. Yom Kippur is described in the Torah as the day of spiritual purification, Ki ba-yom ha-zeh yechapper aleichem mi-kol avonoseichem lifnei Hashem tit’haru, “For on this day He will atone for all of your sins, before Y-H-V-H, God, you will become pure” (Lev. 16:30). The Tanya explained this verse to mean that the purity you will receive will come from before the Tetragrammaton, from the apex of the yud, from the point before the first letter, from the level of yechidah.