Numbers 3:5-10, 38

GOD spoke to Moses. He said, “Bring forward the tribe of Levi and present them to Aaron so they can help him. They shall work for him and the whole congregation at the Tent of Meeting by doing the work of The Dwelling. Their job is to be responsible for all the furnishings of The Dwelling, ministering to the affairs of The Dwelling as the People of Israel come to perform their duties. Turn the Levites over to Aaron and his sons; they are the ones assigned to work full time for him. Appoint Aaron and his sons to minister as priests; anyone else who tries to elbow his way in will be put to death.”

Moses and Aaron and his sons camped to the east of The Dwelling, toward the rising sun, in front of the Tent of Meeting. They were in charge of maintaining the Sanctuary for the People of Israel and the rituals of worship. Anyone else who tried to perform these duties was to be put to death.