The 72nd prohibition is that the Levites are prohibited from performing any Temple service which belongs to the kohanim, and the kohanim from performing any Temple service which belongs to the Levites. The reason for this is that each of these two families, i.e., the kohanim and the Levites, have their own specific types of service in the Holy Temple. Therefore, G‑d (exalted be He) addressed a prohibition to both simultaneously, that each group should perform its own type of service, not the other's. This was told to them in the verse,1 "Each one shall be placed on his service and carry his load."

The prohibition is conveyed in G‑d's statement2 (exalted be He), to the Levites, "But they shall not approach the sacred vessels or the altar, so that they not die." He then continued by saying to the kohanim,3 "[so that they not die,] not they and also not you." The phrase, "and also not you," means "you [i.e., the kohanim] are included in this prohibition. Just as you are com­manded to perform your service, i.e., with the sacred vessels and the altar, so too you are forbidden from performing their service."

The Sifri4 says, "The words, 'They shall not ap­proach the sacred vessels or the altar,' constitutes a prohibition. The words, 'so that they not die,' is the punishment. This teaches only that the Levites have a prohibition and punishment for performing the kohanim's service. How do we know that same applies for the kohanim performing that of the Levites? From the words, 'not they.' [How do I know further that a Levite of] one group [is forbidden to do the work of] the other group? From the words, 'and also not you.' It once occurred that R. Yehoshua ben Chananya tried to help R. Yochanan ben Gudgada [to close the gates of the Sanctuary; whereupon the latter] said to him: 'Go back! You are already guilty of the death penalty since I am from those who take care of the gates5 and you are from those that sing.' " This explains clearly that anyone who serves in a way not meant for him receives a heavenly death penalty.

Similarly, the kohanim may not perform the service of the Levites; but the punishment for doing so is lashes, not death. The Mechilta6 says, "[The verse says,] 'But they shall not ap­proach the sacred vessels or the altar.' One might think that one is punished even for touching them. The verse therefore says 'but' — one is punished only for performing a type of service. This verse only teaches about Levites who perform the service of the kohanim. From where do we derive the prohibition of kohanim performing the service of the Levites? From the words, 'not they and also not you.' " There it also says, "Levites who perform the service of the kohanim are punished by death, but kohanim who perform the service of the Levites only transgress a regular prohibition."