Exodus 19:16 And it came pass on the third day in the morning, that there were thunders and lightnings, and a thick cloud upon the mount, and the voice of a trumpet exceeding loud; so that all the people that was in the camp trembled.
It was evident to all the people that this was God. The Lord God Almighty was here, manifesting Himself in power and glory. Thunder and lightning and thick clouds were common enough, but it was very rare in the Sinai Peninsula. There was something supernatural about the experience, clinched by the sound of an exceeding loud trumpet. A Bible believer will be reminded of the seven thunders and the seven trumpets of Revelation, which brings to mind The Final Judgment.
God is revealing His awesome and holy wrath upon sin and the terrible and eternal judgments upon it. It is no wonder that the sinners trembled in fear. The Lord is showing that He is about to do something really big, so pay attention: He is making a covenant with them and giving the Ten Words on stone tablets. God’s Presence in power and awe got their attention, so that they would take this seriously. He elicited the only response possible: trembling in fear. There would be no doubt in their minds: God means it! This fear of God instills an unwavering faith with no doubting.
There must also come a time (or times) in our life where the Spirit thunders in our heart with the Law, causing a trembling fear. Then He leads us gently to the Gospel where he shows us that our judgment for sin was completely taken up by Jesus. Then we rejoice with exceeding joy. Now we fear and love God so that we keep His Commandments. In God’s hands trembling is good.