Exodus 19: 1 - 2, 9 - 11, 16 - 20
1 On the third new moon after the people of Israel had gone forth out of the land of Egypt, on that day they came into the wilderness of Sinai.
2 And when they set out from Reph'idim and came into the wilderness of Sinai, they encamped in the wilderness; and there Israel encamped before the mountain.
9 And the LORD said to Moses, "Lo, I am coming to you in a thick cloud, that the people may hear when I speak with you, and may also believe you for ever." Then Moses told the words of the people to the LORD.
10 And the LORD said to Moses, "Go to the people and consecrate them today and tomorrow, and let them wash their garments,
11 and be ready by the third day; for on the third day the LORD will come down upon Mount Sinai in the sight of all the people.
16 On the morning of the third day there were thunders and lightnings, and a thick cloud upon the mountain, and a very loud trumpet blast, so that all the people who were in the camp trembled.
17 Then Moses brought the people out of the camp to meet God; and they took their stand at the foot of the mountain.
18 And Mount Sinai was wrapped in smoke, because the LORD descended upon it in fire; and the smoke of it went up like the smoke of a kiln, and the whole mountain quaked greatly.
19 And as the sound of the trumpet grew louder and louder, Moses spoke, and God answered him in thunder.
20 And the LORD came down upon Mount Sinai, to the top of the mountain; and the LORD called Moses to the top of the mountain, and Moses went up.

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