Why will he offer a bull for a Chatas?
Rashi 1 : Perhaps this is in place of the Egel that Aharon offered on the eighth day of Milu'im. The verse teaches that if the Oar was not offered on the eighth day of Milu'im, they should offer it on Nisan 14, in order that the Bayis will be inaugurated for Avodah before Yom Tov. It is upon the Nasi to offer Korbanos of the Mo'ed (17).
Radak: We must say that this will be a new Korban in the future. The Torah did not say to offer a Par Chatas on Mo'adim, only a Se'ir Chatas! Also the seven bulls and seven rams each day of Pesach are unlike the Torah says (to offer two bulls, one ram and seven lambs each day). Also the Minchah is unlike the Torah says (three Esronim for each bull, two Esronim for each ram and one Isaron for each lamb).
Malbim: This is a Hora'as Sha'ah for Chinuch [of the Bayis]. The Par Chatas is not to atone for the Mizbe'ach and Mikdash ? this was done in the previous days! Rather, it is to atone for himself and all commoners.
Rashi: Blessed is Chanina ben Chizkiyah. If not for him, they would have put Sefer Yechezkel in Genizah, for it seems to contradict Torah. He brought 300 barrels of oil up to an attic (for light at night) and expounded to resolve the contradictions (Menachos 45a). However, we do not know what he expounded about this.
