On the morning of the third day there were thunders and lightnings and a thick cloud on the mountain and a very loud trumpet blast, so that all the people in the camp trembled. Then Moses brought the people out of the camp to meet God, and they took their stand at the foot of the mountain. Now Mount Sinai was wrapped in smoke because the LORD had descended on it in fire. The smoke of it went up like the smoke of a kiln, and the whole mountain trembled greatly. And as the sound of the trumpet grew louder and louder, Moses spoke, and God answered him in thunder. 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 Moses went up. (Exodus 19:16–20, ESV)
Coming soon, the feast of Weeks also known as Shavuot or Pentecost.