Christianity is not about moralism, and Christian fiction shouldn’t be either. Christianity revolves, not around good behavior, but around God’s mercy shown to man in the death and resurrection of Christ. However, even though we know this to be theologically true, I think we struggle to remember this as we go about our daily lives, and one of the places where we really struggle to remember it is in our engagement with the arts in general, but as fiction is our topic, we’ll limit our reflection here to that.
I’m constantly surprised at how often fictional stories are judged to be Christian or not, based more or less on how well the characters behave themselves. Of course it is true that morality matters - God has taken great care to expound in some detail the moral laws which flow from and are an extension of His own character. It is also true, though, that the Bible itself is full of flawed men and women whom God used almost despite of rather than because of their moral triumphs. However, when Christian writers incorporate flawed heroes into their stories, men and women with moral failings of any significance, they are often left open to charges of having given dubious testimony to their Lord.