In Exodus chapter nineteen, verse sixteen, claps of thunder and flashes of lightning on the third day came to pass with a thick cloud upon the mountain and a voice so loud that the people of Israel trembled. Mount Sinai was altogether on a smoke because the Lord descended upon it in fire, and the smoke thereof ascended as the smoke of a furnace, and the whole mount quaked. And the Lord spoke out of the core of the fire: the people could hear the voice of the words but saw no similitude, only hear a voice.
The manifestations accompanying God’s visitation had several goals: to demonstrate God’s holiness, power, and transcendence. To instill faith in God and institute the authority of His servant, Moses. To establish the fear of God in the hearts of the people so that they might not sin. To impress upon the people that judgment and death would result in willful disobedience to God. God made the Israelites aware that He’s always near and watching.
Today, many believers claim to be followers of God but do not follow His Word and what it says in the Bible. They have the form of godliness but deny the power thereof. Why the thunders and lightning on the third day upon the mountain? God loves His people and wants them to take Him seriously. If God had just given the Word to His servant Moses, they probably would not ponder it and paid much attention.
Sometimes leaders of a group of people will eventually have to put their foot down to get the message across to the team. They show passion for the folks to understand the importance of following instructions and not taking it lightly. The Israelites experienced how severe God was by the reaction of their shaking on the mountain.