(Mishnah): Seven days before Yom Kipur we separate the Kohen Gadol from his house to Lishkas Parhedrin, and we prepare another Kohen in place of him, if a Pesul will occur to him;

R. Yehudah says, we prepare even another wife for him, lest his wife die, for it says "v'Chiper Ba'ado u'V'ad Beiso'' - Beiso is his wife.

Chachamim: If so [you are concerned for death], there is no end to the matter!

(Gemara) Opinion #1 (R. Ba citing R. Yochanan): We learn [separation of the Kohen Gadol for seven days] from "Ka'asher Asah ba'Yom ha'Zeh'' - these are the seven days of Milu'im. "Tzivah Hashem'' - for all generations. "La'asos'' - this is Se'ir Yom Kipur'';

Question: Perhaps it is rather Se'ir Rosh Chodesh!

Answer (R. Ba): "Lechaper Aleichem'' - a Kaparah like this (the Milu'im). Just like this, Aharon's Kaparah was by itself (his Chatas and Olah - Vayikra 9:7) and his sons' Kaparah was by itself (with that of Bnei Yisrael, through Korban ha'Am), also here (what we learn from Lechaper Aleichem) Aharon's Kaparah is by itself and his sons' is. (Se'ir Rosh Chodesh is for everyone.)

Opinion #2 (R. Yonah citing Bar Kaparah): We learn [separation] from "Ka'asher Asah ba'Yom ha'Zeh'' - these are the seven days of Milu'im. "Tzivah Hashem'' is burning the Parah [Adumah];

Source: It says here "Tzivah Hashem'', and it says there [about Parah Adumah] "Zos Chukas ha'Torah Asher Tzivah Hash-m Leimor.''

Opinion #2 (cont.): "La'asos'' - this is Se'ir Yom Kipur'';

Question: Perhaps it is rather Se'ir Rosh Chodesh!

Answer: We answer similar to R. Ba (above). "Lechaper Aleichem'' - a Kaparah like this. Just like this Kaparah (the Milu'im) was Kosher only through the Kohen Gadol, also here [we learn to] a Kaparah Kosher only through the Kohen Gadol.