Halakhah sobre Números 18:3

That the priests not be involved in the service of the the Levites and the Levites in the service of the priests: That the priests not be involved in the service of the Levites and the priests in the business of the Levites, but rather each one does the work designated for him, from that which is written (Numbers 4:19), "each man to his service and his load." And the language of the prevention that comes about this is that which is stated about the Levites (Numbers 18:3), "but to the vessels of the Holy and to the Altar they shall not approach"; and afterwards the verse returns to speak about the priests, "and they shall not die, also they and also you" - meaning to say with this that you too, you are included in this negative commandment. Since just like the Levites are prevented from their work [when it is not assigned to them], so too are you prevented from your work [when it is not assigned to you]. And the language of the Sifrei on Numbers 18:3: "'To the vessels of the Holy and to the Altar' [is the] warning; 'and they shall not die' is the punishment. I only [know] that the Levites are punished and warned about the service of the priests; from where do I know [the same] about the priests [doing] the service of the Levites? [Hence] we learn to say, 'also you.'" And we have found (Sifrei on Numbers 18:3) that Rabbi Yehoshua ben Chananiah wanted to help Rabbi Yochanan ben Gudgodah in the closing of the doors, [and] he said to him, "Go back, as you are already liable with your soul (life), as I am from the gatesmen and you are from the singers." Behold, it is elucidated that any Levite that does work in the Temple that is not his designated work is liable for death by the hand of the Heavens. And so [too,] the priests are warned not to approach the work of the Levites. However, if they did transgress this, they are not killed, but rather [get] lashes. And they said in the Mekhilta (Sifra Zuta), "'To the vessels of the Holy and to the Altar they shall not approach' It is possible that they would be liable if they touched [them]. [Hence] we learn to say, 'but' - for the work they are liable, and not for touching. I only [know] about the Levites for the [work of the] priests, from where do I know about the priests for the [work of the] Levites? [Hence] we learn to say, 'also you.'" And there it is said that the Leivtes on that of the priests is [punished] with death, but the priests on that of the Levites is only with [the consequences of violating] a negative commandment.