Here's an example: Vodun, or what we commonly call "voodoo." From birth, many practitioners of Hatian Vodun are taught that death is similar to life, and that the human soul is a tangible thing that can be possessed or captured. It is taught that when a person dies, an evil shaman (a Bokor, BTW) can capture that soul, raise your body, and you will be his slave forever. Sound familiar? That's where we get the legend of zombies from. So when someone figured out that they could use the neurotoxin in a fugu fish to poison someone into a death-like trance, they used it to enslave people by waving a jar over their faces when they awoken and yelled "I've got your soul! You're mine now!" They were brought up believing it as truth, and so, to them, it is truth. Does it sound ridiculous? Does it sound any more ridiculous than what anyone else believes?
There are hundreds of religions in the world, with thousands of little off-shoots to choose from. It is my opinion that, as writers, we have the responsibility to pot ray existing religions accurately in narration. We have the responsibility to show the world through a clear lens. We can use characters to show attitudes about religions, but in narration, I feel we must be fair.
So how do you go about using religion? Well, you have two choices. Either go with an existing religion, or create your own. Both methods require exhaustive research, and the readers will get the attitude of the religions from the way the characters speak about them. But there are advantages and pitfalls to using both methods.
If you're working with a pre-existing religion, you'd better do your homework. Even if you are a practicing member of that religion, you need to make sure you've got it right. Why? Because people feel very strongly about their beliefs. Think about the things you care about. Think about the one thing that, if someone got it wrong, it would make you kitten-punching angry. Now multiply that level of fanaticism by about 1,000,000, and that's how much people care about their religions. More to the point, you, as the writer, want to come across as a competent, intelligent individual. So study up. Get it right. How? Research. Go to a place of worship. I don't care if it's a coven meeting or a temple or a synagogue, go there and observe. Talk to the people of that religion. Seriously. Have you ever known a religion authority figure (priest, monk, preacher) who didn't want to talk about his religion? If all else fails, Google is your friend. Just make sure you do your research and get it right. Remember that you, as the writer and narrator, need to be respectful. The characters can be just as crazy as they want, but make sure to differentiate between the normal practitioners and the extremists. Remember, you only hear about the crazy ones on the news. You never hear about normal folks.
On the other hand, you could build your own religion. Careful, though. It's not as easy as it seems. Your religion needs to have tenants, followers, faithful and zealots. What's the central message? What's the point? Is it similar to an existing religion? Is it totally new? What type of religion is it? See, religions were, for the most part, borne out of the societies they were a part of due to circumstance. For example, many pagan and heathen (meaning "from the heath") religions were agriculture based because the original practitioners of them were farmers. So what type are you building? Is it monotheistic or polytheistic? Is it ancestor worship, like in Japan? Is it agriculture based, or rooted in the so-called "secret histories?" Is it a "secret" (occult) religion?
To answer those questions, you need to ask yourself a few more.
- What role does the religion play in your society?
- What rolls ors the religion play for your character?
- How devout is your character?
- How many other characters follow this religion?
- How many oppose it?
Using religion as a literary device is an imposing task. If you need to include one as a key plot point, don't half-ass it. Dig in, get up to your elbows, and do the work. In the end, what you'll get is a richer character and a more complete world for your reader. And you don't need to dedicate chapter after chapter, page after page of defining every minute detail about the religion. Keep it in your head and give the reader just enough that he or she can smell what you're cooking.
As always, these are just my personal methods. They're not the end-all-be-all way of doing things. The bottom line is that if it's right for the story and right for the character, it's good. That's really all you need to know.