How did the opening passage of the book (first paragraph up to first chapter) lead you to anticipate the tone of the book?

The first passage of Good Omens is as follows:

"It was a nice day.

All the days had been nice. There had been rather more than seven of them so far, and rain hadn't been invented yet. But clouds massing east of Eden suggested that the first thunderstorm was on its way, and it was going to be a big one."

This passage gives the setting, Eden, and lets us know that the book will have some sort of religious theme to it. However, it doesn't take itself seriously. This isn't a deep philosophical book, it's philosophical, and occasionally has lapses of depth, but always under the facade of a humorous book. It actually is hilarious. This first paragraph, even the first two sentences, set the hilarious tone for the rest of the book. "It was a nice day. All the days had been nice." Of course all the days had been nice; they're in Eden. I don't know what the term for this voice or tone is, but in my head Terry Pratchett and Neil Gaiman are saying "Duh" in more eloquent ways and that is their tone. They have this sort of dry humor throughout, and its hilarious. I was able to predict their tone after reading this very first passage. I love the use of the word "invented" instead of, say, "created." Invention is a scientific process, and I love the irony of using it to describe Creation. It makes me giggle.