Numbers 4:5

4:5 When it is time for the camp to journey, ¹  Aaron and his sons must come and take down the screening curtain and cover the ark of the testimony with it.

Numbers 18:7

18:7 But you and your sons with you are responsible for your priestly duties, for everything at the altar and within the curtain. And you must serve. I give you the priesthood as a gift for service; but the unauthorized person who approaches must be put to death.”

[4:5]  ¹ tn The Hebrew text uses the infinitive construct in an adverbial clause of time; literally it says “in the journeying of the camp.” The genitive in such constructions is usually the subject. Here the implication is that people would be preparing to transport the camp and its equipment.