One of the most perplexing acts of Avoda found in the Mishkan is described in this week's Parsha, as the Kohen draws lots and identifies one of the Seirim as a scapegoat – the שעיר לעזאזל - which is to be sent out into the wilderness. Neither the function of this sending out nor the fate of the scapegoat is clear; the only thing of which we can be sure is that this animal is not a Korban and that the entire ceremony is shrouded in mystery.
In his comment on this, Ramban cites a Midrash in Bereishit Rabbah, which identifies the Seir with Esav (after all, Esav is identified in the Chumash as an איש שעיר and his people eventually merged with the nation of Seir). The Midrash continues explicating 16:22, ונשא השעיר עליו את כל עונותם אל ארץ גזרה, parsing the word עונותם (their sins) as עונות תם (the sins of the simple one) - a clear reference to Yaakov. The Midrash is apparently suggesting that an understanding of Yaakov and Esav is at the core of the process of the scapegoat, yet what the exact connection is left unclear.
When we look at the story of Yaakov and Esav, we notice that Yaakov succeeded initially in receiving his father’s blessing by mimicking Esav, or, perhaps, in becoming Esav. In donning the goatskin clothes (notice: goat = Seir!) he took on the very attributes that had been identified with his older brother. Yaakov, the תם, or smooth one, became hairy like Esav. It was through this act of deception that he initially got the blessing, and that act of deception is the עון תם, the sin of the smooth one.
Anything positive emerging from that act of deception must be seen as an ill-gotten gain and must be disposed of before genuine blessing can be earned. The process of atonement for the Jewish People on Yom Hakippurim demands that we divest ourselves of anything gained through deception as an integral aspect of earning true expiation and blessing. Toward that end we take the Seir, representing Yaakov’s posing as Esav and all that was profited from that, and send it away to a desolate place, signifying that we are prepared to give up the benefits of deception.
Aside from the national implication of the act, there is personal meaning as well. Yom Hakippurim is a day on which we are to explore who we truly are; in other words, a day in which we are to shed the masks and disguises we wear. It is only through an honest confrontation with the self, with no airs or self-deception, that we can truly merit the forgiveness of the day. As the nation confronts its own past, so too, the individuals within, the net result being the personal and national redemption from that which we brought upon ourselves.