Bible Verses About Priests: All except seed of Aaron excluded from being

You are to appoint Aharon and his sons to carry out the duties of cohanim; anyone else who involves himself is to be put to death."

to remind the people of Isra'el that an ordinary person, not descended from Aharon, is not to approach and burn incense before ADONAI, if he wants to avoid the fate of Korach and his group - as ADONAI had said to him through Moshe.

You and your sons with you will exercise your prerogatives and duties as cohanim in regard to everything having to do with the altar and within the curtain. I entrust the service required of cohanim to you; the unauthorized person who tries to perform it is to be put to death."