1) ENTERING THE AREA BETWEEN THE ULAM AND MIZBE'ACH
QUESTION: The Gemara discusses Perishah, the requirement that everyone stay away from a certain part of the Beis ha'Mikdash while the Kohen performs a certain Avodah. RASHI (DH Ma'alos d'Oraisa) explains that according to all opinions, the only Perishah required mid'Oraisa on days other than Yom Kippur is the requirement to stay out of the Heichal while the Ketores is offered inside the Heichal on the Mizbe'ach ha'Penimi. The requirement to stay away from any place outside of the Heichal, such as the area between the Ulam and Mizbe'ach, is only a Gezeirah mid'Rabanan.
Why did the Rabanan enact a Gezeirah that one not enter the area between the Ulam and Mizbe'ach while the Ketores is being offered in the Heichal? Rashi explains that the Rabanan feared that if one would be permitted to enter the area between the Ulam and Mizbe'ach, he might accidentally walk into the Heichal (an Isur d'Oraisa) while the Ketores is being offered. Therefore, they decreed that one must stay far away from the Heichal.
If the Rabanan enacted a Gezeirah in order to prevent a person from accidentally entering the Heichal, then why did they not make such a Gezeirah on Yom Kippur as well? On Yom Kippur, the Torah forbids any person from entering the Heichal while the Ketores is being offered in the Kodesh ha'Kodashim (44a). Nevertheless, there is no prohibition, not even mid'Rabanan, against entering the area between the Ulam and Mizbe'ach. Why did the Rabanan not enact the same Gezeirah for Yom Kippur that they enacted for the rest of the year when the Ketores is being offered in the Heichal?
(a) The RITVA (44a) points out that Rashi (DH Aval b'Sha'as Haktarah) addresses this question when he says that since the outer Mizbe'ach is "far from where the Ketores is burned on Yom Kippur" (i.e. the Kodesh ha'Kodashim), there is no need to prohibit entry into the area between the Ulam and Mizbe'ach.
Why is there no need to enact such a prohibition? Even though that area is far from the Kodesh ha'Kodashim where the Kohen Gadol burns the Ketores, it is not far from the Heichal, which one is still forbidden to enter mid'Oraisa!
The Ritva explains that the only fear is that one will attempt to peer into the Heichal in order to see the Avodah of the Ketores, and as he does so he will inadvertently enter the Heichal. On Yom Kippur, though, when the Ketores is burned in the Kodesh ha'Kodashim, a person will not attempt to peer into the Heichal because he knows that there is nothing there to see. Since he will not try to peer inside, there is no fear that he will accidentally enter the Heichal.
(b) The TOSFOS HA'ROSH understands that Rashi means that nobody will enter the Heichal when the Kohen Gadol offers the Ketores on Yom Kippur, because everybody stands with much greater awe of the offering of the Ketores in the Kodesh ha'Kodashim. When Rashi writes that it is far away from the place of the Haktarah, he is explaining why the Rabanan did not prohibit one from entering the area between the Ulam and Mizbe'ach on Yom Kippur as a preventative measure for the rest of the year (if one is permitted to go there on Yom Kippur, perhaps he will mistakenly think that he is permitted to go there on other days). Rashi is saying that people will not confuse Yom Kippur with any other day, because on Yom Kippur the Ketores is offered far away from the Ulam, and thus there is no reason for people to confuse it with the offering of the Ketores in the Heichal during the rest of the year.
(c) The RITVA and TOSFOS YESHANIM suggest another answer. On Yom Kippur, the Rabanan preferred not to prohibit one from standing between the Ulam and Mizbe'ach, because they wanted other Kohanim to stand there as sentinels to watch the Kohen Gadol in the Heichal. This was done so that the Kohen Gadol would know that his actions were being observed and, if he was a Tzeduki, he would be afraid to place the Ketores on the coals before his entry into the Kodesh ha'Kodashim.