Commentaries:
What power! Those people were terrified when they heard the voice of God. It shook them to their very being—and that was God's purpose!
This, of course, "is written for our admonition," as Paul says in Romans 15:4. Moses writes this to impress upon us the connection between "voice," "words," and "power." So powerful is the voice of God that it is a miracle that they lived through hearing it! None of us have ever had to face anything like this, but this was written for us so that we could make the connection between "voice," "words," and "power."
When we think of power, we almost always think of the Holy Spirit, but Jesus said, "The words that I speak to you, they are spirit, and they are life"—they have power. When God gave His spirit, He gave it accompanied by the sound of a mighty, rushing wind—like a hurricane that bends and breaks things in its path, the same forces that create and form lightning and thunder! So we have "voice," "words," "power," and "spirit" linked in a process that will affect life.
John W. Ritenbaugh
Unity (Part 4): The Voice of God