"Small Gods" is the thirteenth book in Terry Pratchett's Discworld series.
Pratchett's Discworld universe contains a plethora of gods. The vast majority of these gods are tiny, swarming invisibly and unnoticed in the desert. But a few gain a following of worshippers, which increases both the size and the power of these fortunate gods. One such god was Om, who was so powerful in the country of Omnia that the priests who ruled the country would tolerate the worship (or even mention) of any other god. Om would typically manifest himself as a giant bull; but, when the story opens, he has somehow been transformed into a small tortoise. Om is preoccupied with his reduction in status - from powerful being to to tiny reptile - and with avoiding the talons of hungry eagles circling overhead.
One of Om's problems is that the people of Omnia don't really believe in him - they only go through the motions of their religion out of fear of the priests and the mysterious Quisition, who capture, judge, and torture accused heretics. Another of Om's problems is that he cares very little for the lives and fates of those who worship him - he only desires their faith because it brings him greater power, but he cannot even remember the names of his own prophets.
While struggling in his tortoise form, Om encounter Brutha, an illiterate student/servant with a good heart. Brutha is the only one in Discworld who can see or hear Om because he is the only one who believes in him without the threats from the Omnian church. Brutha is troubled to discover his god is not omnipresent or omniscient or caring or even polite. But he agrees to help him return to his former glory.
Small Gods is filled with quirky characters and witty prose. Like all the Discworld novels, every scene overflows with silliness. Pratchett describes a philosopher with the following:
His philosophy was a mixture of three famous schools -- the Cynics, the Stoics and the Epicureans -- and summed up all three of them in his famous phrase, "You can't trust any bugger further than you can throw him, and there's nothing you can do about it, so let's have a drink."
Or this witty exchange between the leaders of two countries:
"Slave is an Ephebian word. In Om we have no word for slave," said Vorbis.
"So I understand," said the Tyrant. "I imagine that fish have no word for water."
But Small Gods also biting satire about the dangers of religious zealotry and the emptiness of blindly following tradition. With Small Gods, Pratchett reaches beyond making us laugh and makes us think.