Numbers 8:19
And I have given the Levites as a gift to Aaron and to his sons from among the children of Israel, to do the service of the children of Israel in the tabernacle of the congregation, and to make an atonement for the children of Israel: that there be no plague among the children of Israel, when the children of Israel come nigh unto the sanctuary.
Numbers 8:19 belongs to the instructions concerning the purification and service of the Levites, who were assigned to serve in the sanctuary on behalf of the children of Israel. Numbers 8 explains the arrangement for Israel's sacred service, that the Levites were set apart to serve Aaron and his sons in the tabernacle, as prescribed in the book of Moses.
The wilderness tabernacle is here called the sanctuary, meaning the sacred place of worship and building that God claimed as His dwelling place where His service was performed, not a land. It is one of fifty-six places where this building is so called. God gave the Levites as a gift to Aaron and to his sons, setting them apart and consecrating them to do the service of the children of Israel in the tabernacle on their behalf.
Though the priests were also descended from Levi and their labors were interwoven, the two offices were distinctly segregated and in no sense similar or interchangeable. The Levites were the priests' appointed servants to do the manual work of the sanctuary for the people. Their service for Israel included making atonement for the people. That manual work was to provide the showbread, to make ready the meat offering, to bake the unleavened cakes, and to cleanse day by day the courts and chambers of the Lord's house and all its vessels, to stand by at the morning and evening sacrifice with words of praise and thanksgiving, and at the set feasts, new moons, and Sabbaths to burn sacrifices in any number as ordered by the priests, and to be responsible for the safety of the tabernacle.
In the wilderness they were consecrated to care for the sanctuary and to bear it and all its sacred vessels when Israel traveled and the camp set forward during the forty years of wandering. The sanctuary as first given was made portable so it could be taken down, carried on the journeys, and erected wherever the divine presence in the cloud by day and pillar of fire by night directed Israel to pitch camp. By this service and atonement, there would be no plague among the children of Israel when they came near and approached the sanctuary.