What you have come to is nothing known to the senses:
not a blazing fire, or a gloom turning to total darkness,
or a storm; or trumpeting thunder or the great voice speaking ....
The whole scene was so terrible that Moses said: I am afraid, and was trembling with fright...
You have come to God himself, the supreme Judge ....
Make sure that you never refuse to listen when he speaks...
That time his voice made the earth shake,
but now he has given us this promise:
I shall make the earth shake once more and not only the earth but heaven as well.

- Hebrews 12