Moses went up the mountain to pray to god, God said in three days he himself would speak to the people of Israel.
God gave Moses the 10 commandments
Then on the third day lighting and thunder hit the ground, and the sky went black. the volcano started to rumble and shake.
do not be afraid
Then himself God was heard calling Moses like a loud trumpet.
Now God speaks to Moses a says "i am the lord your God, and these are my commandments, to be obeyed by all my people.
When the people of Israel saw the thunder, lighting and smoke the would not come near. but then Moses told them "do not be afraid". "God has come to us so that we may learn his ten commandments and keep ourselves free of sin."
do not be afraid!
The people still did not agree to go up the mountain to see God, so Moses went up the dark, cold and smoky mountain alone and when he reached the top and he went to the dark cloud on the summit and there was God.