The premise of "Twilight of the Money Gods" is, as the subtitle, "Economics as Religion and how it all Went Wrong" suggests, is that economic theory (and the wealth supposedly generated) has usurped religion (and therefore God) as a focus of worship. As Rapley points out, you can't prove the existence of either. You simply have to believe. That pile of bills in your wallet only has a certain value because you (and your bankers) believe that it does, just as a crucifix or other religious symbol represents belief in a higher power.
Although the religious anologies seem somewhat forced (major economic theorists are prophets, their major proponants high priests, and breakaway theorists form new sects), Rapley does point out that the rise of imperialism in 15th century Europe that allowed the creation of a newly wealthy and therefore more independent bourgeoisie to lead to a much more secular life, was helped along by the teachings of Martin Luthor who advocated that personal faith could save individuals without the need for intervention by the clergy. New universities were created, funded by this new secular wealth, and the children of the bourgeoisie were no longer likely to study theology, but art, science and the classics. Daily life was no longer focused on the Church.
The strength of this book though, lies in its overview of Western economic theory and philosophy from the late 1700s to the present. The ideas of Adam Smith, Thomas Malthus, Frederich List, John Stuart Mill, Karl Marx, Georg Hegel, on up to John Maynard Keynes and Milto Friedman etc. are explained in layman's terms, along with their effects on the politics of the day. I read a library copy of the book (so popular that I waited 17 weeks for it!), but a copy of my own on the shelf would be useful to dip back into now and again to remind myself of certain economic concepts.