I've heard this question a good deal, and undoubtly it is one for many Christians who are seeking to write.
So far as I see it, writing is not religious though the writer may be religious; in the same way, a band may not be religious, but may be composed of religious people. The point of writing fiction is to present a world, and for the author to press something to readers to think of. With this in mind, and the reality of how miserable (and luminously beautiful) this world is, there should be no limit to your presentation, so long as your intention is to do good, which isn't hard at all. Some of the nastiest movies and books have wonderful endings that reveal an excellent and necessary intention by the author or writer. You should feel free to present a world of debauchery, bad language, agitation, hedonism, what have you -- so long as there is an end to it. And people tend to relate better to realistic stories -- that is, stories with nastiness in them -- than they do stories that are pretty and idealistic. So long as there is an end and intention throughout that the author sustains, whether it be presenting a single protagonist who is Christ-like, or what have you, you are doing God's will, even in writing.