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 16:5, 40
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 18:7
But only you and your sons shall attend to your priesthood for everything concerning the altar, and for what is inside the veil, and you are to perform that service. I am giving you the work of the priesthood as a gift, but any outsider who comes near the sanctuary must be put to death."