When the camp is ready to be moved, the Kohathites will be responsible for carrying the sacred objects and the furnishings of the sacred tent. But Aaron and his sons must have already covered those things so the Kohathites won't touch them and die.
When the Israelites are ready to move their camp, Aaron and his sons will enter the tent and take down the curtain that separates the sacred chest from the rest of the tent. They will cover the chest with this curtain,
It is like what happens when a man goes away for a while and places his servants in charge of everything. He tells each of them what to do, and he orders the guard to keep alert.