Warning: I'm writing this assuming you've seen the film. There are spoilers. (Then again, C.S. Lewis thought it was a vulgar pleasure to want to know what happens in a story.)
"Harold," Dustin Hoffman's remarkable character flatly states, "I'm sorry. You are going to die."
This moment becomes the crucial one, the turning point for boring IRS agent Harold Crick, masterfully played by Will Ferrell, surprisingly. He must decide if he will do the brave action and allow the potential meaning of the story of his life to become actuality. The cost, however, is his life. Will he lay down his life for the sheep?
At the end of the film we find that he does. Fully knowing the cost of sacrificing his body for the sake of a boy accidentally fallen in front of a bus, he does it anyway. The "author" of his story, Karen Eiffel, then brings him back to life. Her book isn't quite as good, as Professor Hilbert, Hoffman's character, points out. She counters, however, that Harold is precisely the kind of human being one wants to keep alive. He is a good man, who will do what is right despite the cost to himself.
During the scene in which Eiffel explains her choice to Prof. Hilbert, the Lord's words in Matthew 16:25 boomed in my mind: "For whoever would save his life will lose it, but whoever loses his life for my sake will find it." Harold, willingly giving his life for the little boy, found his life by the grace of Miss Eiffel. He walks the path of the disciple and he is found true in the judgment.
The gospel, the good news, is that this pattern, slightly spiritualized, actually works. Jesus really does offer life for those who would die to themselves, for those who would put someone else's interest about their own.
Now, the objection that I immediately thought of and found dissatisfying at first, was that the story wasn't as good with Harold's miraculous recovery at the end. This is the place where the analogy of the film breaks down. It doesn't cost a mere mortal like Karen Eiffel anything to achieve her desired ending. She simply rewrote the book. In real life, however, a high price had to be paid. The incarnated God Himself had to go to the cross and die for many. The ending of the book in Stranger Than Fiction leaves us dissatisfied because the grace is too cheap. We know in our hearts that grace is real, but it is not a wrought by a waive of the hand.
In a culture that increasingly embraces nihilism and scoffs at the idea of redemption, it is wonderful to see a story pointing to the deep reality of the universe that grace exists for those who would deny themselves.