One who is not a Kohen must not serve

This mitzvah prohibits non-kohanim from engaging in avodah in the Mikdash. While Levites had their assigned roles and Israelites could bring offerings, only kohanim descended from Aaron were permitted to conduct sacrificial service.

Rambam codifies this law to preserve the sanctity and structure of the Temple service. Allowing unauthorized individuals to serve would violate the divinely mandated hierarchy and dishonor the holiness of the avodah. Sefer HaChinuch stresses that the kohanim were sanctified by Hashem for this purpose, and others may not intrude on their role.

The Torah attaches the severe penalty of death by Heaven (mitah bidei shamayim) to a non-kohen who serves, underscoring the seriousness of maintaining Divine order in the Mikdash. Ramban adds that this mitzvah reflects the covenantal role of the priesthood, ensuring that the avodah is performed with the proper sanctity, order, and reverence.

Commentary & Classical Explanation:

• Rambam (Hilchot Bi’at HaMikdash 9:6–7): Rules that a non-kohen performing avodah is liable to death by Heaven, as the service is the exclusive duty of kohanim.
• Sefer HaChinuch (Mitzvah 392): Explains that Hashem sanctified the kohanim for the avodah, and it is forbidden for others to intrude upon their service.
• Rashi (Num. 18:7): Notes that “stranger” means anyone outside the priestly lineage, even Levites.
• Talmud (Sanhedrin 83b; Zevachim 17b): Discusses the definition of “zar” (stranger) and the severity of the punishment.
• Ramban: Teaches that the prohibition ensures the Temple functions as Hashem commanded, with each group fulfilling its assigned role.