In Likutei Moharan 29 Rebbe Nachman states that complete removal of the stain of sin can only be achieved through rectification the limbs through tikkun ha’bris (rectification of “the covenant” – i.e. sexual sins – or circumcision). Rebbe Nosson now develops this theme.
The above expresses a certain aspect of Yom Kippur. For Yom Kippur was established for forgiveness and atonement – through the tikkun ha’bris that was performed on it, as in the verse: “For on that very/b’etzem day Avraham was circumcised”. Avraham was the first person to engage in tikkun ha’bris; he was the first person to be given a circumcision. And since it was done on Yom Kippur (according to the holy books), this day was then fixed for future generations as a day of atonement and forgiveness – for sins are whitened through tikkun ha’bris. This is the meaning of our Rabbi’s words: “The power/itzumo of the day atones”, for it relates to the verse “on that very/b’etzem day Avraham was circumcised”.
Later on, [after the Sin of the Golden Calf], Hashem was gladly appeased by Moshe, saying “I have forgiven you”. This is also an aspect of forgiveness for p’gam ha’bris/blemish of the covenant (sexual transgression). For the Sin of the Golden Calf was also p’gam ha’bris, as our Sages teach: “The Jewish nation only worshipped idols in order to permit themselves openly engaging in forbidden relations”. And since p’gam ha’bris was forgiven and rectified at that time, hence it was fixed for forgiveness for future generations.
And this is the explanation of “I have forgiven you, according to your words”. “According to your words” – because according to the tikkun/rectification of speech, so is [the measure of] forgiveness (see LM 29).
Consequently, all the Temple service of Yom Kippur was done solely by the Cohen Gadol/High Priest. For cohanim/priests embody the concept of sh’miras ha’bris/guarding of the covenant (i.e. sexual purity), as in (Devarim 33:10): “They shall teach Your judgments to Ya’acov and Your Torah to Yisrael… (33:9) for they kept Your commandment and Your b’ris/covenant”. It also says regarding cohanim that “they shall be holy”, where holiness is delineated by our sages as being “in any place that you find a fence for immorality”. They are warned regarding marital matters more than other Jews. And the Cohen Gadol is cautioned with even more prohibitions and bears greater holiness, as it says: “He is holy to his G-d”. His holiness lies in his purity in sexual matters. He is warned regarding forbidden marital matters more than non-cohanim – and even more than cohanim.
Therefore the Temple service of Yom Kippur, which atones for sins, is only valid if done through the Cohen Gadol. For the Cohen Gadol is the only one that can raise ha’da’as/holy awareness (the synthesis of loving kindness and judgment) and draw upon the Heavenly force that whitens our sins, through the kedushas ha’bris/the holiness of the Covenant [i.e. sexual purity].
This relates to the verse regarding the Cohen Gadol (Vayikra 21:10): “upon whose head is poured the oil of anointment”, which is an aspect of da’as elyon/Supernal awareness. The Cohen Gadol attains this through the kedushas ha’bris, as indicated by the proximity of the verse dealing with kedushas ha’bris: “He may not marry a widow or a divorcee…for he is holy”. For one matter is dependant on the other.
Correspondingly, they would go to great lengths to guard the Cohen Gadol from an involuntary bodily emission, since the entire Yom Kippur service and its forgiveness component depend on this. Thus, they would stay awake the entire night. For this is tikkun ha’bris through the subjugation of [the concept of] sleep that relates to the idea of targum (translation of Hebrew into one of the 70 root languages), as explained elsewhere.
In addition, it is imperative that the Cohen Gadol be married, since an unmarried man has a quality of p’gam ha’bris. Consequently, the death of Aharon’s sons, whose sin was being unmarried, is mentioned in the Torah next to the Yom Kippur service (and is actually read on Yom Kippur). Their unmarried state made them unqualified to enter the place that they did and caused their removal. For it is only possible to enter the Holy of Holies and draw upon the da’as elyon through complete tikkun ha’bris.
When it is mentioned elsewhere that the sons of Aharon had sinned by entering in a drunken state, it refers to the concept of “wine enters and secrets emerge” (as explained in LM 29). For everything is the same idea and one is dependant on the other.
Hilchos Yom HaKippurim 1