Numbers 4:17-20

The LORD said to Moses and Aaron, “Don’t let the Kohathites be cut off from the Levites. Do this for the Kohathites so that they may go near the Most Holy Place and not die: Aaron and his sons must go in and show each Kohathite what to do and what to carry. The Kohathites must not enter and look at the holy things, even for a second, or they will die.”