Christian fiction or inspirational fiction denotes stories centered on characters who find religious faith, or rediscover or deepen it through their experiences in the plot. I have seen a few Jewish inspirational novels, but this field is mostly supported by evangelical Christian publishing houses. I’m not sure what most publishers would do with an inspirational novel about finding one’s faith in Buddhism or Wicce: probably judge it as a quirky lead character in another genre of novel: women’s fiction, mainstream, contemporary fantasy.
Inspirational fiction exists as a genre because some publishers do nothing else, not because it’s terribly different than related non-inspirational forms. A Christian mystery is on the same template as a regular one, as far as structure of the mystery, but it must also include one of the inspirational templates of faith found or renewed, for secondary characters if not the main detectives.
In Christian or inspirational romance, religion is important in a romance story. It also requires that the romance be a sweet one: lust and indecency are not what the readers are here for.
You can have inspirational historical romance or inspirational histfi straight. You can have inspirational Westerns, Napoleonics, and of course the first centuries CE have long been almost entirely the domain of stories about early Christians (Ben Hur, A Tale of the Christ; The Silver Chalice; The Living Wood).
You can also have inspirational fantasy, like the work of C. S. Lewis.
Two traps must be avoided when writing inspirational fiction, to keep it real and appealing (this is what the publishers like Tyndale say).
First, write a story, not a tract. Avoid one character lecturing another at length. Especially avoid “preaching to the choir,” expostulating to a believer. This is worse than “As You Know, Bob” or The Dreadful Scene, because the reader probably knows all this as well as the poor lectured character does (this fiction is only 5% read by anyone but committed Christians, fewer than men reading romance fiction). Discussions that present both sides interest the reader much more, especially those rare ones not converted. Yes, you must actually know what real objections real people bring up and how to answer them. Learning this will deepen your own convictions and contact with your faith, so it’s not unpleasant or irrelevant. You also provide your reader with answers for their own conversations.
Don’t reform a resistant or shallow character only as a result of a lecture. Any missionary may wish it were this easy, but knows it isn’t. The step-by-step redemption is the main template of this genre.
The second trap is literal deus ex machina endings. Randy Ingermanson’s City of God series held me for two volumes because I wanted to see how he won over his scientistic atheist. He used the ultimate cheat: he had God chat with the atheist. I don’t care how much you believe in miracles, this is past unsatisfying to actively annoying. We want to see how people can lead others to faith by normal means, or how faith can reveal itself to a thinking mind. All DXM does is reduce reader faith, leaving me thinking, “Well, I guess he can’t refute the atheist stance.”
Remember that other plots exist besides “saving non-believers.” A protagonist with shallow, confused, corrupted, or weak faith has a lot of growing to do, which automatically gives you a story readers can identify with.