To put it simply, if a "deeply" Christian author writes about a historical time which contains no overt Christianity, might we not assume it is a pre-Christian setting? Just regarding the setting, I am going to quote the author:
In Letter #211 (1958), Tolkien wrote:May I say that all this is 'mythical', and not any kind of new religion or vision. As far as I know it is merely an imaginative invention, to express, in the only way I can, some of my (dim) apprehensions of the world. All I can say is that, if it were 'history', it would be difficult to fit the lands and events (or 'cultures') into such evidence as we possess, archaeological or geological, concerning the nearer or remoter part of what is now called Europe; though the Shire, for instance, is expressly stated to have been in this region (I p. 12). I could have fitted things in with greater versimilitude, if the story had not become too far developed, before the question ever occurred to me. I doubt if there would have been much gain; and I hope the, evidently long but undefined, gap* in time between the Fall of Barad-dûr and our Days is sufficient for 'literary credibility', even for readers acquainted with what is known or surmised of 'pre-history'.
I have, I suppose, constructed an imaginary time, but kept my feet on my own mother-earth for place. I prefer that to the contemporary mode of seeking remote globes in 'space'. [...]
* I imagine the gap to be about 6000 years : that is we are now at the end of the Fifth Age, if the Ages were of about the same length as S.A. and T.A. But they have, I think, quickened; and I imagine we are actually at the end of the Sixth Age, or in the Seventh.
Of course, this was written after the fact, and isn't obvious from the text of the book, never mind the film.
redrobot wrote:in the mythology timeline there is no suggestion that christianity wd happen subsequent to what we know
Many readers do detect a prefiguring of Christianity in the story, which is an effect Tolkien was aiming for (one little essay at random