There are no atheists in the modern economy. You may not have God or Buddha in your life, but you very much have faith—in money. I don't mean that you worship money in the greed-is-good sense. No, you have faith in its value. Your trust in it depends on everyone else's, which means that our faith in money's value is really about trust in each other—a belief in shared purpose, or at least a shared hallucination.

Cash, as in banknotes and coins, helps us to maintain that magical...