In its delineation of the avodat Yom Hakippurim, the Torah (Vayikra 16:17) imparts "vekol adam lo yihiyeh be-ohel moed bevo'o le-kaper ba-kodesh ad tzeito" - that while the kohen gadol served in the Kodesh Kodashim during the blood sprinkling of the par and sair sacrifices (16:14-15) and while the ketoret was being consumed (16:12-13), no one was permitted even in the adjacent venue of the heichal. The Talmud (Yoma 44a) extends this principle. Thus, when avodah (the daily ketoret, the blood offerings-matanot of the Yom Kippur korbonot or of the par he'elem davar etc.) took place in the heichal, the adjacent area between the ulam and mizbeach also had to be evacuated. It is intriguing that the verse conveying this puzzling restriction concludes by referring to the expansive atonement accomplished by these most private avodot of Yom Kippur - "vekiper ba'ado u'be'ad beito u'be'ad kol Kehal Yisrael." [This is the most sweeping and inclusive expression of collective forgiveness in the avodah. See 16:6,11- "vekiper ba'ado u'be'ad beito", 16:24-"vekiper ba'ado u'be'ad ha'am", 16:33-"ve-al hakohanim ve-al kol am hakahal vekiper"] What is the significance of this extraordinary privacy requirement and how is it connected to the broad impact of the avodah. Indeed, the Gemara (Yoma 44a) notes that the source verse does not explicitly mention the ketoret, but that the conclusion that refers to the atonement of the entire Klal Yisrael implies it -"eizeh kaparah sheshaveh lo ule'ehav hakohanim ve-kol Kehal Yisrael hevi omer zu haketoret." While some (Chizkuni 16:17) perceives this demand to be a purely technical precaution to avoid the risk of ritual impurity that might not have been subject to the atonement of Yom Kippur, this perspective does not satisfactorily explain the wider application to the avodah in the heichal or the connection to comprehensive atonement.
Rav Hirsch understood this requirement to further cordon off the avodot of the innermost precincts not as a manifestation of elitism or a demand for greater privacy, but actually as an expression of the added relevance and impact of these locations to the rest of the mikdash structure and to the everyday life of Klal Yisrael. In his view, the adjacent venues were inherently linked with and therefore experienced the overflow impact of whatever occurred in the private precincts, and, consequently also needed to be cleared of those who were not directly implementing the avodah. The purpose was not to further isolate or seclude the inner precincts or the elite avodah they hosted, but to acknowledge the fluidity-interconnection of all parts of the mikdash, which technically mandated a wider berth. It is inconceivable, in his view, that distancing the rest of the population was the purpose or goal of this imperative, as all dimensions of the avodah, even the most private, enhance all of the nation and connect to its daily mission in and out of the mikdash. The link between comprehensive atonement and the special role of the ketoret is consistent with this position.
We may posit another perspective to complement Rav Hirsch's approach. Netziv (Ha'amek Davar 16:17) links Chazal's view of the role of ketoret in neutralizing the pervasive transgression of gossip (lashon hara), the ultimate breach of privacy-tzeniut, with the special demand for a further layer of privacy. This idea is supported by the Gemara (Zevachim 88b), "ketoret mekaperet al lashon hara - yavo davar shebechashai ve-yekaper al ma'aseh chashai". Rashi (Zevachim 88b, Arachin 16a) specifically refers to the perishah requirement in this context.
A close analysis of the Gemarot in Yoma and the Rambam's rulings (Hilchot Temidim 3:3,9) establish that while there are other applications of this additional distancing condition, as noted, the primary focus of this special requirement is the ketoret. [See a summary of some of the evidence in Gevurat Yitzchak, ad loc, especially his citation of the Griz, and his analysis of the differences between ketoret and hazaot ha-dam.] Rambam codifies this demand specifically in Hilchot Temidim (not in Hilchot Bait Mikdash), in the framework of his treatment of ketoret (and Chinuch, likewise - no. 103). In that context, he expands to other applications, but in a manner that also accents subtle differences between the primary and secondary applications. The evidence demonstrates that the need for extra privacy, isolation during the ketoret offering is an internal factor and even part of the essential character and definition of this special avodah. Some posit that for this reason, the demand does not constitute and independent mitzvah, as it primarily constitutes a dimension of ketoret itself. Some mefarshim (Rinat Yitchak op cit) speculate that ignoring the adjacent evacuation requirement may even invalidate the ketoret!
The ketoret is perceived as an acutely spiritual form of avodah. The fact that it accentuates the more amorphous, ephemeral sense of smell is consistent with this status. It is hardly a coincidence that great religious crises that also test the boundaries of and relationship to material and spiritual Divine worship revolved around ketoret. Korah's insincere, cynical quest (machloket shelo lesheim shamayim - Avot) to vulgarize Jewish spiritual leadership, even the sacrificial order, anchored in the apparently noble but actually diluting value of "kol ha-edah kulam kedoshim", was decidedly defeated by ketoret. The tragic, sincere but misguided ketoret zarah offered by Nadav and Avihu is perceived by many views in Chazal as an effort to hyper-spiritualize avodat Hashem. Avodat Yom Kippur itself is introduced against the background of that tragic misconception - "achrei mot shenei benei Aharon be-karvatam lifnei Hashem va-yamutu" - as a corrective that both rejected and incorporated elements of that hyperspiritualization. Thus, "bezot yavo Aharon el ha-kodesh" charts a Divinely-guided balanced, multifaceted process presided over by Aharon ha-Kohen and those who will succeed him (16:3, 33). The centerpiece consists of an especially finely ground (dakah min ha-dakah) ketoret that accounts for two trips into the kodesh ha-kodoshim! The extensive protocols, including the oscillation between inner and outer precincts of the mikdash, and all that implies, protect and enable "ki be-anan eiraeh al ha-kapporet"!
It is unsurprising that this ultimate attainment, produced in the highly calibrated framework of five tevilot and ten kidushim, embodying dizzying wardrobe changes signifying the interaction of avodat penim and avodat chutz, engenders a need for excessive tzeniut - seclusion, that it constitutes an important dimension of this singular ketoret itself. Daily ketoret, also subject to this demand for isolation and exclusive presence, mandated and defined its own mizbeah, mizbeach ha-ketoret inside the heichal.
The dialectic between tzeniut- privacy-seclusion and a public posture and comprehensive impact is a singular feature of halachic life. Both methodologies are indispensable, and they need to be complementary to achieve complex, halachically aspirational goals. Chazal note that the first luchot were revealed in the presence of all of Klal Yisrael accompanied by thunder and lightning (kolot u-verakim), but the luchot that ultimately survived were the one's presented to Moshe in seclusion, embodying the quality of tzeniut. Our primary vehicle for prayer is the silent, highly personal, even intimate Amidah, although it is also followed by chazarat ha-shatz, a manifestation of tefillat ha-tzibur. The fact that the hazaot ha-dam and especially the ultra-refined Yom Kippur ketoret demand excessive seclusion and privacy notwithstanding and in conjunction with the public spectacle of avodat Yom Kippur is consistent with this broader phenomenon. Indeed, the selective appropriate manifestations of tzeniut and acute spirituality, exemplified by ketoret, ultimately facilitate comprehensive kapparah for each and all segments of Klal Yisrael - "vechiper baado ube'ad beito u-be'ad kol Kehal Yisrael."