I'm sorry, but that's simply not true of all Christians, including me (I've yet to have a single review describing my novels as "moral instruction" or variants thereof). There are many Christian writers whose faith informs their writing - indeed it is impossible for it not to, just as an atheist writer's worldview informs their writing - but it does not necessarily manifest as moral instruction, especially if - as in Tolkien's case - it was written to deliberately omit it. In my case, the approach I take is to simply write a good story with no intentional message at all. I write about that process in more detail here, if you're interested. :)