What Chatas does he offer?
Rashi (from Mo'ed Katan 15b) #1: The first time he enters the Mikdash to be inaugurated in Avodah, he offers Asiris ha'Eifah (Chavitim) ? "Zeh Korban Aharon u'Vanav 1 " (Vayikra 6:13), like it says in Menachos 51b.
Radak: This is a Chidush in the future ? he will offer a Chatas for his Tum'ah 2 .
Radak (from Mo'ed Katan 15b) #2: A Kohen Gadol offers Asiris ha'Eifah every day 3 . He did not offer it when Tamei 4 . He offers it now, after becoming Tahor.
Radak (from Mo'ed Katan 15b) #3: We infer that while he was Tamei, he was unable to send Korbanos. "Uv'Yom Bo'o? Yakriv" ? he can offer [even via a Shali'ach] only when he is proper to enter.
Malbim: This was needed also in Bayis Sheni. Many old Kohanim returned, who had served in Bayis Rishon. It says so in Ezra (3:12) "v'Rabim meha'Kohanim? Asher Ra'u Es ha'Bayis ha'Rishon 5 ?" Yechezkel teaches that they needed to bring Asiris ha'Eifah again. Since the Bayis was destroyed in the middle, it is as if they begin Avodah afresh. Also in Bayis Shelishi, Yechezkel and other revived Kohanim who already brought Asiris ha'Eifah will need to bring it again.
We find that a Nazir offers Korbanos if he became Tamei. (PF)
Radak: This is astounding. The verse discusses a Kohen Hedyot, who becomes Tamei for relatives! (Why didn't Radak explain like Rashi there, that the verse discusses a Kohen Hedyot, who brings Asiris ha'Eifah the first day that he serves? Perhaps it is this is obvious that he may not do so when Tamei. ? PF)
Chavitei Kohen Gadol are brought even b'Tum'ah (Menachos 76a). However, if there is a Tahor Kohen, the Kohen Gadol may not bring it when he is Tamei. (PF)
The verse proves that many saw Bayis Rishon, but not that they served in it. Seemingly, few served in both Batim, for (a) there were 70 years in between (81 for those exiled with Yechanyah), (b) a minor Kohen cannot serve, and Kohanim did not allow youths below 20 to serve (Chulin 24b), and (c) an old Kohen who quivers may not serve (ibid.) (PF)
