At Mount Sinai, God gave the clear instruction when we can go to him when we hear the Loud voice at the Mountain - And the Lord said unto Moses, Lo, I come unto thee in a thick cloud, that the people may hear when I speak with thee, and believe thee for ever. And Moses told the words of the people unto the Lord. And the Lord said unto Moses, Go unto the people, and sanctify them to day and to morrow, and let them wash their clothes, And be ready against the third day: for the third day the Lord will come down in the sight of all the people upon mount Sinai. And thou shalt set bounds unto the people round about, saying, Take heed to yourselves, that ye go not up into the mount, or touch the border of it: whosoever toucheth the mount shall be surely put to death: There shall not an hand touch it, but he shall surely be stoned, or shot through; whether it be beast or man, it shall not live: when the trumpet soundeth long, they shall come up to the mount - Exodus 19:9-13

But even after the Loud Voice the people of Israelites were forbidden to come close to Mountain - 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. And the Lord said to Moses, Go down and warn the people, lest they break through to the Lord to look and many of them perish - Exodus 19:16-21