How does Terry Pratchett use imagery in Small Gods: A Novel of Discworld?

Imagery:

“Fear is a strange soil. It grows obedience like corn, which grow in straight lines to make weeding easier. But sometimes it grows the potatoes of defiance, which flourish underground.”

“Humans! They lived in a world where the grass continued to be green and the sun rose every day and flowers regularly turned into fruit, and what impressed them? Weeping statues. And wine made out of water! A mere quantum-mechanistic tunnel effect, that'd happen anyway if you were prepared to wait zillions of years. As if the turning of sunlight into wine, by means of vines and grapes and time and enzymes, wasn't a thousand times more impressive and happened all the time...”