Gemara

5a - Suggestion: "Shiv'as Yomim Yilbasham ha'Kohen Tachtav mi'Banav" should require a Kohen Gadol to wear the extra Begadim for seven days and be anointed with Shemen ha'Mishchah for seven days for the sake of inauguration!

Rejection: "Asher Yimshach Oso va'Asher Yemalei Es Yado" - it suffices even if he wore the extra Begadim for seven days and was anointed for one day, or vice-versa.

Toras Kohanim (Emor Perek 1 Parshesa 2:2) Question: What is the source that is suffices even if he wore the extra Begadim for one day and was anointed for one day, even for a short time?

Answer: "Asher Yutzak Al Rosho Shemen ha'Mishchah" - even for a short time; "U'Milei Yado Lilbosh Es ha'Begadim" - even for a short time.

12a: If a Kohen Gadol became Pasul before the morning Tamid, offering the Tamid (in Bigdei Kohen Gadol) inaugurates the substitute;

Question: If the Kohen Gadol became Pasul after the morning Tamid, how do we inaugurate the substitute? (The Bigdei Lavan used for Avodas Panim are like Bigdei Kohen Hedyot!)

Answer #1 (Rav Ada bar Ahavah): The Avnet inaugurates him (he wears a pure linen Avnet; a Hedyot's Avnet contains wool).

Question: This is like the opinion that a Hedyot's Avnet is like a Kohen Gadol's Avnet the rest of the year (i.e. it contains wool). According to the opinion that a Hedyot's Avnet is like the Kohen Gadol's linen Avnet of Yom Kipur, how can we answer?

Answer #2 (Abaye): He wears the eight Begadim and flips over limbs (of the Tamid on the Mizbe'ach, to help them burn faster) with a pitchfork.

This is like R. Chanina, who says that a Zar who flips limbs with a pitchfork is Chayav Misah (it is a proper Avodah that requires Kehunah).

Answer #3 (Rav Papa): His Avodah (of Yom Kipur) inaugurates him (just like Avodah inaugurates Kelim):

Beraisa: All the Kelim that Moshe made were anointed (with Shemen ha'Mishchah) to be Mekadesh them for the Avodah;

Subsequent Kelim are inaugurated by using them for Avodah.

Rishonim

Rambam (Klei ha'Mikdash 4:13): When a Kohen Gadol is being inaugurated, he dons the eight Bigdei Kohen Gadol and removes them each day for seven days. Similarly, he is anointed with Shemen ha'Mishchah for seven days.

Source (Radvaz): Moshe did all the Avodah during the Milu'im because Aharon had to wait until seven days of anointment or wearing the Begadim.

Rambam (ibid.): If he served before wearing the Begadim for seven days or seven days of anointment, his Avodah is Kosher, as long as he was anointed or wore the Begadim at least once (beforehand).

Source (Kesef Mishneh): The Sifra expounds that anointment or wearing the extra Begadim even for a short time suffices.

R. Shimshon and Ra'avad (on Toras Kohanim, ibid.): We include Merubah Begadim, who is not anointed at all. This shows that the Sifra expounds that anointment or wearing the extra Begadim suffices.

Rashi (DH Ein Li) and Ra'avad: This inauguration for seven days is required only before Avodas Yom Kipur.

Source (Radvaz): The Gemara used "V'Chiper Alav Asher Yimshach" to teach that for all generations, seven days of inauguration is not Me'akev. Rebbi and the Ra'avad explain that this discusses only Yom Kipur.

The Rambam holds that the Milu'im are just like Yom Kipur, and we learn about inauguration for any Avodah from the Milu'im.

Kesef Mishneh citing Ri Korkus: Really, the Rambam agrees with the Ra'avad. The Rambam discusses inauguration to do Avodah that requires a Kohen Gadol.

Rashi (5a DH Ribuy) and Ra'avad: This inauguration is to do Avodah for seven days in the eight Begadim.

Source (Sefas Emes 12a DH Lovesh): Abaye requires a proper Avodah while wearing the eight Begadim. This shows that wearing the Begadim without Avodah does not inaugurate (unlike the Rambam).

Rambam (Hilchos Avodas Yom Kipur 1:3): If a Kohen became Pasul on Yom Kipur, whether before or after the morning Tamid, his replacement does not need inauguration. His Avodah inaugurates him.

Question: The Gemara said wearing Bigdei Kohen Gadol different than a Hedyot's inaugurates him. His inauguration is through Avodah according to the opinion that (even) the Avnet of a Hedyot is like Bigdei Lavan of Yom Kipur. The Rambam holds like the former opinion, so why does he say that Avodah inaugurates?

Answer (Lechem Mishneh): The Rambam explains that Rav Ada holds that wearing the Avnet inaugurates, but Rav Papa says that this is not necessary, for Avodas Yom Kipur itself inaugurates him.

Acharonim

Question: Above (5a) we learned from "Shiv'as Yomim Yilbasham..." that seven days of anointment and wearing the Begadim are required l'Chatchilah before Yom Kipur, and from "Asher Yimshach Oso va'Asher Yemalei Es Yado" that b'Di'eved one day suffices. Here, Rav Papa does not require any prior inauguration! And the Rambam rules like both of these!

Answer (Likutei Halachos 4b Zevach Todah DH v'Davka): Rav Papa's law applies only to a substitute when the Kohen Gadol became Pasul. The words of the Rambam 'his replacement does not need inauguration...' support this.

Source (Sifra Acharei Mos Perek 8:4): "V'Chiper ha'Kohen Asher Yimshach Oso" allows any Kohen who will be anointed (to do Avodas Yom Kipur); "va'Asher Yemalei Es Yado" includes Merubah Begadim; "V'Chiper ha'Kohen" includes any Kohen that will be appointed. (Gra - "ha'Kohen" is extra).

Ra'avad: The last inclusion teaches that we must designate a substitute beforehand, and that the designation suffices in place of Meshichah of Ribuy Begadim. The substitute cannot be anointed or wear the Begadim beforehand, for this would cause enmity.

Likutei Halachos (ibid.): Rav Ada and Abaye agree that this is the law mid'Oraisa. They merely seek ways to publicize that he is Kohen Gadol, so it will not look like a Hedyot does Avodas Yom Kipur (which is done in Bigdei Lavan, which resemble Bigdei Hedyot).

Question (Merumei Sadeh DH Pshitah): "Asher Yimshach..." teaches that inauguration is not Me'akev Avodas Yom Kipur. According to the Rambam, this includes Avodas ha'Tamid on Yom Kipur, for the Kohen Gadol must do it. But Tosfos (32b DH Im) holds that mid'Oraisa a Hedyot may do it. If so, what is the source that inauguration is not Me'akev?

Answer (Merumei Sadeh, ibid.): Tosfos (12b DH Kohen) learns from the Yerushalmi that a Kohen Gadol is appointed or deposed verbally. It follows that inauguration is not Me'akev; it is merely a Mitzvah.

Tosfos explains that wearing Begadim special for a Kohen Gadol fulfills Ribuy, and Avodah in such Begadim inaugurates. According to the opinion that Bigdei Hedyot are the same as Bigdei Lavan, wearing Bigdei Zahav is Ribuy; Abaye requires flipping limbs while wearing them to inaugurate.

The Rambam learns from "Asher Yimshach" that Ribuy is not needed on Yom Kipur. Therefore, we must say that wearing Bigdei Zahav is to inaugurate. Abaye discusses flipping limbs, because the Heter to wear Bigdei Kehunah with Sha'atnez is only for the sake of Avodah (according to the Rambam).