And the Lord said to Moses, “I will come to you in a thick cloud, in order that the people may hear when I speak with you and so trust you ever after. Go to the people and warn them … beware of going up the mountain or touching the border of it. Whoever touches the mountain shall be put to death … he shall not live.”
“On the third day, as morning dawned, there was thunder, and lightning, and a dense cloud upon the mountain and … all the people … trembled.” And God commanded, His stormy dark turbulence thundering down His words. “I the Lord am your god who brought you out of the land of Egypt, the house of bondage: You shall have no other gods besides Me.”
Moses spoke to the people, “Be not afraid; for God has come only in order to test you, and in order that the fear of Him may be ever with you, so that you do not go astray. So the people remained at a distance, while Moses approached the thick cloud where God was.”
Exodus 19-20