Why does the Torah refer to the Par of the Kohen Gadol as "ha'Par ha'Rishon"?
Horayos, 13a: To teach us that, in the event that the Kohen Gadol and the Kahal sinned, the Kohen's Par must be brought first. 1
Horayos (Ibid.): It is befitting for the one who is atoning to be cleansed of his sin before he comes to atone for others. See Torah Temimah, note 78, who elaborates.
"Chatas ha'Kahal Hu". What is "Hu' referring to?
R. Bachye: It refers to the Par mentioned at the beginning of the Pasuk.
"Chatas ha'Kahal Hu". Why does the Torah refer to the Par that the Sanhedrin brings as 'Chatas ha'Kahal'?
R. Bachye: It hints that the sin that Yisrael perpetrated in the desert was the bull - as the Midrash writes in Sh'mos Rabah 'They removed one of the four Chayos that support Hashem's throne - as the Navi wrtes in Yechezkel 1:10 "u'Penei Shor me'ha'Semol le'Arbatan". 1
Seforno: Because it would not have occurred had the people not also been guilty of sinning.
Sifra: It is a Binyan Av - to teach us that all communal sin-offerings (such as the Se'irei Avodas-Kochavim) must be completely burnt (outside the camp).
"Chatas ha'Kahal Hu". What is "Hu" coming to preclude?


