One thing I always used to completely ignore when writing fantasy was religion. I'm an atheist and don't really think much about religion during everyday life; and in popular culture these days, religion is generally sidelined. It's not part of the everyday lives of TV show characters or film heroes.
But after studying the ancient world for the last three and a half years, one thing that has struck me is that the ancient Greeks and Romans really made the worship of their gods a big thing. Competitions like the Olympic Games and the Great Dionysia (a theatrical competition) were all about the gods. The Olympic Games took place at a sanctuary; the Great Dionysia was named after the god it was intended to praise, Dionysus, who was the god of theatre (and also wine, grapes, dancing naked in circles, etc). The Romans had shrines to the household gods in their homes. Gods were part of myth and legend, the stories they told each other in the evenings; at parties they poured libations of wine on the floor to the gods before they started drinking; mosaics, vase paintings and sculpture depicted gods and in many cases were dedicated to the gods at sanctuaries all over Greece and Italy. Votive dedications were given to the gods by merchants in exchange for a safe journey equal to one tenth of the profits from that journey.
In the modern world, religion is the source of both unity and conflict. Even within one religious group there are wildly divergent views on certain issues - condoms, female priests, abortion, issues of sexuality.
And yet, I realised a little over a year ago, I tend to ignore religious considerations when I'm writing. But religion is something which affects us quite a bit, even if we aren't religious. It can provide a character with a motive for acting in a certain way, create instant conflict or harmony between two characters or groups, or be used to explain a character's prejudices, expectations, hopes or fears. And more than that, it can add believability to a world and can be used to demonstrate precisely how much an event had affected your characters when something catastrophic leads a character to either embrace religion or question it, or change the way they worship.
So what I want to know is, do you include religion in your novel? What is the nature of that religion - a single god, many gods that all require worship, many gods from which each character can choose which one or two to worship, no gods but certain forces of nature, like Water or Wind, which people worship without personifying them? How does it affect your characters? How does it influence the world, the prejudices of the people who inhabit it, and their attitudes?
In my current story, I've got a set of seven gods, each linked to certain aspects of nature and human existence - Linsear, for example, is the goddess of water, rain, streams, rivers, lakes, cleanliness, purity and virginity. Shuve is the god of all things ancient - mountains, ruins and old buildings, cemeteries and the dead, and traditions. Six of the seven gods have had an associated prophet at some point in the last 400 eyars before the story (I'm holding the last one for a future story), and this prophet had a profession in some way linked to the god or goddess - so Linsear's prophet was a washerwoman.
I apply this religion to the story in several ways. Their names are given to the days of the week - Shuve's day, Linsear's day etc. Certain annual festivals crop up, one of them forcing my characters to choose, after a virus has killed three quarters of the population, whether to risk the now unsafe wilderness to go to a pilgrimage site unguarded by the men of the group in order to attend a women only festival, or whether to remain safe at their farm. One character, whose brother, now dead, was a priest, experiences a crisis of faith and questions the very existance of the gods, only to be shunned for expressing such doubts by other characters, who fear the wrath of the gods will follow his disbelief and destory him.
I also have a whole host of swears and oaths based on the gods and the prophets - Dehbu's breath is one, referring to the prophet of the goddess of light, fire, glass and mirrors, who was a glassblower and is a sort of patron saint-esque figure to people with certain skilled trades. Swear phrases like this are selected according to the pre-virus profession or status of the swearer. Gods names are not used to swear, exactly, but are used to emphasise urgency - "run as though Sernald himself was following you" is something I've used, referring to the god of madness, rabies, beer, cats, and opiates and other drugs, in this case in his role as the god of madness. This way I can avoid using realworld swearwords, I can give greater emphasis to the word "bastard" (which crops up a lot since illegitimacy is a big thing to my characters, particularly if the parents are from wildly different statuses, and one of my characters is the illegitimate son of the dead king and a woman from a skilled trade background), and I can avoid certain phrases which are based upon Christian ideas, such as the phrase "go to hell". Instead, I can have something like "Sernald take you for his prophet" (Sernald being the god who hasn't had one yet).
And woah what a long post. I'd love to hear how other people deal with religion in their stories.