Deuteronomy 10:8
At that time the LORD set apart the tribe of Levi to carry the ark of the covenant of the LORD, to stand before the LORD to serve Him, and to pronounce blessings in His name, as they do to this day.

Deuteronomy 17:12
But the man who acts presumptuously, refusing to listen either to the priest who stands there to serve the LORD your God, or to the judge, must be put to death. You must purge the evil from Israel.

Exodus 28:1
Next, bring near to you your brother Aaron from among the Israelites, along with his sons Nadab, Abihu, Eleazar, and Ithamar, to serve Me as priests.

Numbers 3:10
So you shall appoint Aaron and his sons to carry out the duties of the priesthood; but any layman who approaches the tabernacle must be put to death."

Numbers 16:5, 9, 10
Then he said to Korah and all his followers, "Tomorrow morning the LORD will reveal who belongs to Him and who is holy, and He will bring that person near to Himself. The one He chooses He will bring near to Himself. . . .

Numbers 17:5-9
The staff belonging to the man I choose will sprout, and I will rid Myself of the constant grumbling of the Israelites against you." . . .

Numbers 25:13
It will be a covenant of permanent priesthood for him and his descendants, because he was zealous for his God and made atonement for the Israelites."