What relation does the Sufi proverb (the epigraph) have to the book?

"The epigraphs to The Handmaid's Tale frame the narrative that follows. The third epigraph is a Sufi proverb: "In the desert there is no sign that says, Thou shalt not eat stones." The proverb can be interpreted in multiple ways in relation to The Handmaid's Tale; given the novel's preoccupation with the structures of power, it suggests that power can be secured by controlling access to scarce resources. In the desert, stones are not a resource, but water and food are. Therefore, no law, moral or social, will forbid anyone to eat stones in the desert. The proverb can also refer to desire: power can be secured by controlling the routes to satisfy desire." (1)