3 They are to be responsible to you and are to perform all the duties of the tent, but they must not go near the furnishings of the sanctuary or the altar. Otherwise both they and you will die.

Read Numbers 18:3 Using Other Translations

And they shall keep thy charge, and the charge of all the tabernacle: only they shall not come nigh the vessels of the sanctuary and the altar, that neither they, nor ye also, die.
They shall keep guard over you and over the whole tent, but shall not come near to the vessels of the sanctuary or to the altar lest they, and you, die.
But as the Levites go about all their assigned duties at the Tabernacle, they must be careful not to go near any of the sacred objects or the altar. If they do, both you and they will die.