Numbers 3:38
38 Those who were to camp before the tabernacle qon the east, before the tent of meeting toward the sunrise, were Moses and Aaron and his sons, rguarding the sanctuary itself, to protect1 the people of Israel. And sany outsider who came near was to be put to death.
Numbers 8:19
19 And I have ogiven the Levites as a gift to Aaron and his sons from among the people of Israel, to do the service for the people of Israel at the tent of meeting and to make atonement for the people of Israel, pthat there may be no plague among the people of Israel when the people of Israel come near the sanctuary.”