Answer: Creation is the sole realm of God.
Shelley argues that the method, or mechanism, by which God created the world is stupendous, or fantastic. Therefore, when a human attempts it, it comes across as mocking, due to the flawed nature of our methods. This mocking is horrible, because the man who attempts it wants to be seen as a god, or at least as capable and powerful as God himself. Therefore, the consequence of these actions must be horrible too.
