Ezra 2:62
They made search for their record among the lists of families. Their names were nowhere to be found. So they were looked on as unclean and no longer priests.
Numbers 3:10
Appoint Aaron and his sons to serve as priests. Anyone else who tries to do the priests' duties must be put to death.
Leviticus 21:21-23
If a descendant of the priest Aaron has a physical defect, he must never bring sacrifices by fire to Jehovah. He has a defect. He must never bring food to offer to God.
Numbers 16:39-40
The priest Eleazar took the copper incense burners that had been brought by those who had been burned to death. The incense burners were then hammered into thin metal sheets to cover the altar.
Numbers 18:7
Only you and your sons may do the work of priests, everything done at the altar and under the canopy. This is my gift to you: You may serve me as priests. Anyone else who comes near the holy place to do this work must die.
Ezekiel 44:10-14
But the Levites, who went far from me when Israel went astray, who went astray from me after their idols, will bear the punishment for their iniquity.