The temple service of Yom Kippur is only valid if performed by the High Priest. (Yoma 32b)
And Moshe said to Aharon, “What did this people do to you, that you brought so great a sin upon them?” (Shmot 32:21)
Aharon is the one who led the people to the brink of destruction in the episode of the golden calf. Does it really make sense to entrust him with the survival of the people on Yom Hakippurim?
The answer is, well… yes.
The Talmud Sanhedrin 7a states:
And when Aaron saw the golden calf, he built an altar before it. What did he actually see? — R. Benjamin b. Japhet says, reporting R. Eleazar: He saw Hur lying slain before him and said [to himself]: If I do not obey them, they will now do unto me as they did unto Hur, and so will be fulfilled [the fear of] the prophet, Shall the Priest and the Prophet be slain in the Sanctuary of God? and they will never find forgiveness. Better let them worship the golden calf, for which offence they may yet find forgiveness through repentance.
The Talmud records an opinion which praises Aharon’s involvement in the sin. He was willing to sacrifice himself; stand with the people in their breach of God’s covenant in order to save them from an even worse violation which would almost certainly have brought God’s wrath and destruction upon them. For Aharon, love of the people trumps the Covenant with God.
According to the great Hassidic master, Yehudah Aryeh Leib Alter (1847–1905), the Sfat Emet, it is precisely this skeleton in Aharon’s closet which makes him uniquely qualified to serve as High Priest.
In Rashi: “Draw near to the altar” [Moshe speaking to Aharon] ’Why are you reluctant/ashamed? You were chosen because of this.’ This is why the Shechina did not dwell in the mishkan by the merit of Moshe but only by the merit of Aharon, because Aharon was a penitent (Ba’al Teshuva). .. I believe that this is the reason that it happened that Aharon was involved in the sin [of the golden calf] so that he could redeem the people’s sins through his love. (Shemini 5641)
It is precisely the shame and lack of worthiness which Aharon feels as a consequence of his complicity in the sin of the golden calf that qualifies him to be the chosen one to repair the broken relationship between the children on Israel and God.
The one who stands before God on Yom Kippur on behalf of the people, must be of the people; his fate bound to theirs, paradoxically, even at the expense of his own relationship with God.