Exodus 19:20-22

The 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. Then 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]. Also 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].”