Terry Pratchett 
Small Gods 
(Discworld Novel 13)

» You should do things because they»re right. Not because gods say so. They might say something different another time. »
Religion is a competitive business in the Discworld. Everyone has their own opinion and their own gods, of every shape and size — all fighting for faith, followers, and a place at the top.
So when the great god Om accidentally manifests himself as a lowly tortoise, stripped of all divine power, it»s clear he»s become less important than he realised.
In such instances, you need an acolyte, and fast. Enter Brutha, the Chosen One — or at least the only One available. He wants peace, justice and love — but that»s hard to achieve in a world where religion means power, and corruption reigns supreme . . .
»An intriguing satire on institutionalized religion corrupted by power . . .» Independent

»Deftly weaves themes of forgiveness, belief and spiritual regeneration» The Times
The Discworld novels can be read in any order but Small Gods is a standalone.