1. The Gemara explains why the Kohen Gadol was taken to Beis Avtinas.
2. The Gemara quotes the Mishnah in Midos which discusses the chambers of the Beis ha'Mikdash.
3. Part of the job of the Sanhedrin was to decide whether a Kohen's lineage was appropriate for him to serve in the Beis ha'Mikdash.
4. The Kohen Gadol immersed in a Mikvah five times during the Avodah of Yom Kippur.
5. There is a discussion about whether the Kohanim are the agents of Hashem or the agents of the people.
A BIT MORE
1. He was taken there in order for him to learn about offering the Ketores, which was made in Beis Avtinas.
2. For example, the Sanhedrin convened in the Lishkas ha'Gazis.
3. If he was found to have pure lineage, he would leave the Sanhedrin wearing white and promptly join his fellow Kohanim. If his lineage was found lacking, he would wear black and leave the Beis ha'Mikdash.
4. He also washed his hands and feet ten times during the day.
5. The practical difference is whether a person who swears not to derive benefit from a certain Kohen may have that Kohen offer his Korbanos. If the Kohen is Hashem's Shali'ach, then the Kohen may offer his Korbanos on his behalf, but if he is the public's Shali'ach, then the Kohen may not offer his Korbanos on his behalf.