The Kohathites were entrusted with the care of the holy furniture when it was on the move
upon God’s instruction, whereas Moses, Aaron, and his sons were entrusted with that responsibility when the tabernacle was stationary. The sons of Aaron would serve specifically to protect the people of Israel
(ESV), or more accurately, to meet the needs of the sons of Israel
(Numbers 3:38).
38 Those who were to camp before the tabernacle on the east, before the tent of meeting toward the sunrise, were Moses and Aaron and his sons, guarding the sanctuary itself, to protect the people of Israel. And any outsider who came near was to be put to death.