The beginning of Parshat Acharei Mot discusses the service that Aharon and future Kohanim Gedolim must perform on the holiday of Yom Kippur. But Yom Hakippurim is discussed in Parshat Emor. Why is this section placed here?
Harav Yehuda Shaviv, in his Sefer Misinai Ba, differentiates between the two sections, thus answering the question. He explains that in Emor, only the parts of Yom Kippur pertaining to the nation as a whole are discussed, while Acharei Mot goes into the details of the Kohen Gadol’s service. His Avodah is an extension of the laws pertaining to Tumah and Tahara, impurity and purity, which has been presented since Parshat Shemini. This is highlighted by the fact that last week’s Parsha ended off (15:31), “VeHizartem Et Bnei Yisrael MiTumatam, VeLo Yamutu BeTumatam, BeTamam Et Mishkani Asher BeTocham,” “You should separate Bnei Yisrael from their impurity, and they won’t die via their impurity if they contaminate My Mishkan that is among them.” Acharei Mot continues this theme in the new topic of Aharon’s Yom Kippur Avodah. Right after mentioning the deaths of Aharon’s sons, the Pasuk states that if Aharon stays away from the Kodesh HaKadashim, “VeLo Yamut,” “He will not die,” as an otherwise necessary punishment. The parallel phrasing of “VeLo Yamutu” and “VeLo Yamut” in these two segments highlights the fact that both sections are indeed connected in their themes of Tumah and Tahara.