It’s Paul’s approach that I find interesting here as well. He basically tells his listeners that he didn’t come with big, fancy words, but with the basic concept of a crucified Lord. It was the story of a God who humbled himself, and was humiliated by the powers of this world. It was the story of a God who died for those he loved. It was the story of a Christ who presented his weaknesses to the world to show them the strength of his desire to redeem them. And Paul did all of this while he, himself, was afraid, trembling in the fear of his own weaknesses. But that’s what Paul wanted. His approach was to let others see the power of God in his actions, and not in his fancy and persuasive words.
In the age of Jesus, it’s not like you could dismiss a voice talking from heaven as someone playing tricks on you with a wireless lapel mic and a hidden loudspeaker. That just wasn’t a possibility. So these people had to dismiss the voice from heaven as thunder, even though they heard the voice, and what it said. They dismissed the voice as thunder because they did not want to believe, or be confronted with the truth.