Exodus 19:20-22

20The Lord came down on Mount Sinai, to the top of the mountain; and the Lord called Moses to the top of the mountain, and he went up.

21Then the Lord spoke to Moses, “Go down, warn the people, so that they do not break through [the barriers around the mountain] to the Lord to see [Me], and many of them perish [as a result].

22Also have the priests who approach the Lord consecrate (sanctify, set apart) themselves [for My sacred purpose], or else the Lord will break forth [in judgment] against them [and destroy them].”