Originally Posted by EatingPie
Pretty much every aforementioned book -- Narnia, Ben Hur, Quo Vadis -- don't sit solely in the "Christian Fiction" genre. They're famed works of fantasy and historical fiction, and would easily be found even if you were filtering Christian Fiction.
I think there's a decided distinction between works which happen to incorporate Christianity-related history or themes or simply have such as a background, perhaps due to being written in a timeframe when public espousal of religious mentions was more common in otherwise secular fiction or perhaps because the author felt like exploring them*, and works which are written specifically for a particularly Christian audience†.
The former are more-or-less intended for general reading, so the themes, while there, may not be all that strong or "preachy" because they're really more about the storytelling potential in such, rather than reaffirming faith or guaranteeing a "clean" read for people looking for those things.
The latter have more definite boundaries due to the expectations the particular market audience has for at least a minimum adherence by the label (no on-screen sex, no swearing, "good" main characters should be in line with their religious viewpoint and not violate tenets of the faith, etc.), so the books can end up being rather different in tone sometimes, even if the overall quality and other story aspects may be roughly the same, just the same as someone buying steamy erotic romance in certain subcategories will have expectations of what should and shouldn't show up in the story.
* Such as Paulo Coelho's Brida
, a mystical mashup of paganism and Christian scripture which I recently read.
† Not necessarily all modern: e.g. The Pilgrim's Progress
, which the Little Women
girls were reading.