Torah Portion: Acharei Mos
“בזאת יבא אהרן אל הקדש…” (ויקרא טז ג)
It is a positive commandment that the kohen gadol execute the entire Yom Kippur service, following the correct sequence of the offerings, confessions, the sending off of the [Azazel] goat and the rest of the service. It is thus written: With this shall Aaron come into the Sanctuary etc. (Vayikra 16:3), and in that portion the Torah presents all of the elements of the Yom Kippur service.
Among the roots of the mitzvah is that, among the kindnesses of God towards His creatures, He set aside for them one day of the year as a day of atonement for sins, alongside their repentance. For if there were no such day, and people’s sins would go on accumulating year after year, the entire world would end up deserving destruction. To sustain the world, the Holy One set one day of the year for the atonement of the sins of those who repent.
This commandment applies when the Holy Temple stands. Nowadays, when due to our sins we do not have the Temple, nor a kohen gadol, nor offerings — it is the practice of all Yisrael to serve Hashem through prayer and supplication, as it is written, let our lips substitute for bulls (Hoshea 14:3).