Chazal derive from the fact that the Kohen Gadol may not leave the Mikdash that he is to perform the avodah, service, even while he is an onan, mourner prior to the burial of a close relative. This is in contrast to the Kohen Hedyot, who may not perform the avodah as an onan. The simple reason given for this is that while one is at the heightened state of grief, the mind is not in control. The despondency that envelops a person at such a time disqualifies the Kohen Hedyot from performing the service, since he no longer has the proper mindset essential for carrying out his mission properly. The Kohen Gadol, on the other hand, is admonished not to leave the Sanctuary. The Sanctuary must dominate his consciousness and reign over his emotions so that he does not even momentarily divorce himself from his lofty mission.
Horav Shneur Kotler, z.l., notes the distinction and special demand placed on the Kohen Gadol. He asserts that the capacity to retain the correct frame of mind crucial for carrying out the priestly service is a requisite of Kehunah Gedolah. This is the interpretation of “from the Sanctuary he shall not leave.” The Kohen Gadol must rise above all worldly events and remain totally kadosh and attached to his avodah. Indeed, as Horav Kotler notes, the ability to remain calm and serene during the most anxious and frightening moments is the hallmark and function of an adam ha’shaleim, a man who has achieved spiritual and moral perfection. Even as he encounters other people and is confronted with mundane challenges, he always remains within the confines of the Sanctuary. Indeed, he becomes the embodiment of the Sanctuary as it permeates his entire essence.