Exodus 19:21-25

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].” Moses said to the LORD, “The people cannot come up to Mount Sinai, because You warned us, saying, ‘Set barriers around the mountain and consecrate it.’ ” Then the LORD said to him, “Go down and come up again, you and Aaron with you; but do not let the priests and the people break through [the barriers] to come up to the LORD, or He will break forth [in judgment] against them [and destroy them].” So Moses went down to the people and told them [again about God’s warning].