What did the Chatas atone for?
Rashi: It atoned for Kever ha'Tehom 1 and for Tum'as Safek.
What is the significance of the Sa'ir?
Rashi (in Pasuk 22, citing R. Moshe ha'Darshen): It atoned for the sale of Yosef, where they Shechted a goat.
Ramban (in Pasuk 2, citing Bamidbar Rabah): It atoned for Yehudah bringing Yosef's shirt [dipped in a goat's blood] to Ya'akov.
Rosh (in Pasuk 12): It corresponds to Eisav, who is called "Ish Sa'ir" - in Toldos Bereishis, 27:11). 1
The angels asked why he is remembered together with Tzadikim, to which Hashem replied that he is mentioned for a Chatas in Acharei-Mos Vayikra, 16:22 which will bear the sins of his fathers, as the Pasuk writes there - "ve'Nasa ha'Sa'ir alav es Kol Avonosam".
