Personal faith is a primal motivator in a person’s life and inseparable from who a writer is. A Christian is charged to share the Good News. If those beliefs don’t show up in a 90,000 word novel, then something important is missing. The author isn’t writing from the gut, not expressing his real self—in a sense, hiding from the reader.
I’m not trying to suggest that fiction should preach, though there have been some dramatic examples of that. Pilgrim’s Progress comes to mind as do more recent novels from the likes of Frank Peretti. Others have used allegory, like the great fiction of C. S Lewis.
Personally, I enjoy reading between the lines and discovering the writer more indirectly, perhaps by something in the story line or through a particular character. It may be a mere impression—a subtle connection with the author’s way of thinking.