Jack Lewis - burly, beery Ulsterman, fellow of Magdalen College, specialist in Renaissance literature and already, by the early 1940s, a well-known religious broadcaster - took a much more excited view of additions to the Tolkien menagerie. Often discouraged, his colleague, soulmate and - for a period in the 1930s - spiritual mentor had been tramping wearily through the spacious literary vistas of the The Lord of the Rings. Without Lewis's enthusiasm as its first hearer, and first critic, the trilogy might never have come to completion.
Then, a couple of years years later, the poles switched. Tolkien's epic labour spurred Lewis to write the seven tales of the Chronicles of Narnia in a blaze of energy and invention from 1948 to 1953.
Now the two fantasy sequences - so similar in origin, so utterly different in mood - will inevitably be paired again. Adaptations of the Narnia books have several times reached the stage, and the studio, since they became required reading for millions of children half a century ago. Animated versions of Narnia surfaced in 1967 and again in 1979 (the latter won an Emmy award in the US). In 1989, the BBC's television series was widely judged definitive; and Adrian Noble's dramatisation for the RSC packed theatres and thrilled critics in 2001.
Yet the Lewis estate had, since the writer's death in 1963, consistently rebuffed attempts to bring the landscapes of Narnia into live-action cinema, fearful that Hollywood would ignore or distort its underlying Christian framework, and especially suspicious of the Disney empire and all its works. (Oddly, Lewis himself had adored Snow White and the Seven Dwarfs when he saw the Disney cartoon in 1939.) There were even rumours that Hollywood planned to make the evacuee children, whose adventures the Narnia novels tell, escape not from Blitz-hit London but from earthquake-struck Los Angeles. Sacrilege!
Then Harry Potter happened - as, of course, did Peter Jackson's all-conquering screen vision of The Lord of the Rings. And Philip Pullman, a militantly secular counterpart to Lewis the stubborn champion of "mere Christianity", went into battle with the His Dark Materials trilogy. Pullman fought, and still fights, very deliberately on Lewis's own ground. The scholarly Oxford ambience, the love of eerie Nordic mythology, the child pilgrims in search of truth, the treacherous grown-ups, the animal spirits, the glimpses of another world older, deeper and more magical than this one: you might conclude that Pullman parks his anti-authoritarian, pro-Enlightenment tanks on every one of Lewis's most cherished lawns.
Pullman has often spoken of his disgust at the exclusion of one of the four Pevensie children, Susan, from paradise at the end of the stories. She has started to become, not a sexless angel, but a young woman interested in evil snares such as "nylons and lipsticks and invitations". The relevant scene at the close of The Last Battle, when the children die in a train crash in this world, does leave a sour taste on any impious palate. But maybe Lewis felt uneasy with it, too. He later told a worried correspondent that perhaps Susan "will get to Aslan's country in the end - in her own way"; after all, there is "plenty of time for her to mend". Mend what? Pullmanites will ask.
So, with Narnia outflanked and overshadowed, the estate thought again. The film rights eventually went to Walden Media, created by the mogul Philip Anschutz. The first episode, The Lion, the Witch and the Wardrobe, opening across the world in a snowstorm of hype on 8 December, is directed by Andrew Adamson, maker of both Shrek films. One of Lewis's stepsons, Douglas Gresham, has monitored the development of the Walden films. (The other, David, has nothing to do with the estate.)
Gresham, a former Tasmanian sheep-farmer and Australian broadcaster, has acted as vigilant keeper of the Lewis flame throughout the production. Anschutz, whose deep pockets at last allowed Disney to green-light a project that other studios had rejected on grounds of cost (about $150m) is an oil and railway baron whose passion for the Lewis novels has its roots in a conservative, Presbyterian outlook.
So, next month, Liam Neeson (as the all-suffering, all-redeeming saviour-lion, Aslan), Tilda Swinton (as the wintry, demonic White Witch) and even Dawn French (as that domestic goddess Mrs Beaver) will lead the four child principals across the frozen land at the back of the wardrobe and through the opening instalment of Lewis's parable of loss, quest and salvation. The landscapes of New Zealand will reprise the acclaimed role of inspirational backdrop they played in Jackson's Tolkien trilogy. And, yes, the Disney studio will at last get its name above the Narnia title as joint producer.
On the platform in my Tube station, two posters currently stand side by side. One announces the opening of The Lion, the Witch and the Wardrobe. The other celebrates a new edition of Pullman's His Dark Materials novels. The battle of belief, and unbelief, has been joined.
Many Lewis worshippers, and more than a few Lewis sceptics, will be scrutinising every scene to see how far the theological sinews of the stories have survived. It seems likely that general uplift will stand in for dogmatic detail. Adamson has spoken vaguely of his admiration for a literary source that "resonates with such themes as truth, loyalty and belief in something greater than yourself". It hardly sounds like a Ratzinger-style call to spiritual arms.
Would Lewis have fretted too much about the potential dilution of his message? Probably not. The Narnia journeys amount to both more, and less, than a pre-adolescent pilgrim's progress - even though Lewis actually kicked off his career as a fiction writer in 1933 with a satirical update of Bunyan, The Pilgrim's Regress.
One common but flawed way of contrasting Tolkien and Lewis pits the purely "epic" conception of The Lord of the Rings against the narrower, "allegorical" style of the Narnia novels. Now, it's certainly the case that Tolkien, a secure lifelong Catholic, never felt the need to evangelise directly through his books of fantasy. In fact, he disliked allegory, and his painful falling-out with Lewis from the late 1940s can - to some degree - be laid at the door of his distrust of surreptitious sermonising in the Narnia mode.
Lewis, by contrast, had lost his Ulster-Anglican faith in youth. His conversion to non-sectarian, traditional Christianity came only in the early 1930s - in part because of the example and friendship of Tolkien himself. A famous night-time walk with Tolkien around the grounds of Magdalen College in September 1931 had led Lewis to the brink of belief.
Then, in a very Home Counties replay of the Road to Damascus a few weeks later, he took a trip to Whipsnade Zoo with his beloved brother Warren ("Warnie"), and with Janie Moore, the much older woman with whom Jack Lewis lived in a loving but still-controversial relationship for more than 30 years. As Lewis put in baldly in his memoir, Surprised by Joy: "When I set out I did not believe that Jesus Christ is the Son of God, and when we reached the zoo I did." There, he saw a bear he liked, and named him Bultitude. For Lewis, humanised animals and the spiritual life always did go paw-in-paw.
So the reformed atheist became a militant apologist for orthodoxy. Although he loathed socialism, and all "progressive" ideals, Lewis hijacked many of the propaganda techniques of mid-century Marxism in famous Christian manifestos such as The Screwtape Letters and The Problem of Pain. With their slick populist gift for slogan, debating-point and caricature, these books - and the wartime radio broadcasts that won him a huge lay audience - actually embarrassed some of Lewis's more theologically learned Christian friends.
Intellectually speaking, the much-loved crusader for "mere Christianity" suspected that he might have feet of clay. That doubt turned into certainty on one traumatic day in 1948. At a meeting of the Socratic Club, the philosopher Elizabeth Anscombe - a follower of Wittgenstein - laid into the arguments in Lewis's book Miracles, with its simple-minded and old-fashioned dichotomy between "naturalist" and "supernaturalist" ways of explaining the world. Or rather, she trounced and trampled them beyond repair. Worse, Anscombe was no unregenerate atheist, but a Catholic, and a strong, intellectual woman to boot - always a menace to Lewis's self-esteem.
After Anscombe's mauling, Lewis wrote almost no more religious treatises. Instead, the passions and intuitions of fiction became the prime vehicle of his faith. You might argue that Anscombe - a professional, not a pub and common-room philosopher - destroyed Lewis as a thinker and made him as a writer.
The Narnia books do not, in fact, succeed terribly well as a strict allegory. Too much atmosphere and imagination gets pleasurably in the way, from the Victorian streets where Professor Kirke grows up to the fabled peaks of Archenland. It may be that the violent and exotic southern land of Calormen does at some level reflect a traditional Christian fear of Islam and its rival culture. But what matters is the vigour and colour of Lewis's creation, which makes doctrinal nit-picking fairly redundant.
The world of Narnia represents far more than scriptural stories shifted many latitudes further north. As Lewis's best biographer, AN Wilson, argues, it resembles far more "the inside of Lewis's mind, peopled by a rich enjoyment of old books and old stories and the beauties of nature, but always threatened by a terrible sense of loss, of love's frailty." If they wish to, non-religious readers can always choose to treat the redemptive message of the Narnia books as background music rather than principal theme. It seems likely that the movies will favour this inclusive, fuzzy-at-the-edges approach.
And Lewis knew more than enough about loss. In 1908, when he was the nine-year-old son of a solicitor in the Belfast suburbs, his mother Flora died of cancer. He began his relationship with Janie Moore, 26 years his senior - probably first as lovers, then as partners who played the roles of mother and son - after Janie's son, and Jack's friend, Paddy died in the final months of the First World War. Jack and "Minto" (as he called her) had lived together in Oxford from 1920. In 1930, they bought a house along with brother "Warnie". Janie's long illness and death (in 1951), and Jack's meeting with his future wife, the American Joy Gresham, form the tumultuous emotional backdrop to the writing of the Narnia sequence.
Most famously for the posthumous Lewis cult and its devotees, his intense autumnal affair and marriage with the witty, headstrong, don-shocking Joy ended when she died (again of cancer) in July 1960. Thanks to Shadowlands - first a book by Brian Sibley, then a stage play and TV and cinema films scripted by William Nicholson - this chapter in the Lewis legacy has probably reached almost as wide a public as The Lion, the Witch and the Wardrobe itself.
Joy has been played by Claire Bloom and Debra Winger; Jack by Joss Ackland and Anthony Hopkins. As a late-flowering love story, this has the works (the waterworks, many damp-handkerchiefed viewers would say). And its conclusion promoted a short book that perhaps deserves to last even longer than Narnia: A Grief Observed. From the heart-clutching opening sentence ("No one ever told me that grief felt so like fear"), it can be warmly recommended to people of any or no religious belief. Yet, when Lewis submitted the manuscript under a pseudonym to Faber, it took TS Eliot himself to save it from oblivion after a sniffy reader's report.
Lewis, once so attached to strength of argument, now both valued and embodied depth of feeling. Love and loss softened the dogmatist - and the losses, thanks to Elizabeth Anscombe, included that of his intellectual pride. Yet he remained to his death (on the day of Kennedy's assassination in November 1963) the deep-drinking, heavy-smoking Belfast bruiser who resembled - to AN Wilson - a "red-faced pork butcher in shabby tweeds".
Today, you can still savour the public Lewis style - of saloon-bar "common sense" yoked to deep but often hidden erudition - in media appearances by Professor John Carey, who knew Lewis in Oxford in the late 1950s. Yet this bluff manner always told only half the story. Students of Lewis such as Kenneth Tynan, who revered him from a political and personal vantage point totally alien to his own, saw and responded to something richer and deeper.
The scandal-seeking creator of Oh! Calcutta! was, at his request, buried to the accompaniment of words by Lewis; words that consider the beauties and pleasures of life as no more than second-best reflections, "the echo of a tune we have not heard, news from a country we have never visited". From a philosophical point of view, this is not Christianity - or not "mere Christianity" - so much as Neo-Platonism, the ancient and recurrent doctrine that our everyday world faintly and falsely mimics a truer, purer one. And Lewis the Renaissance expert had become a sort of Neo-Platonist before he ever converted to Bible-based belief.
It could be that the creation of Narnia shocks or upsets at a level beyond the enduring quarrels between Lewis's religious fans and his secular foes - because it suggests the illusory nature of "real" existence. Indeed, "Shadowlands" is Aslan's own term for the everyday world beyond Narnia. So it seems more than apt that a vast new audience will soon share this vision via flickering images in darkened halls across the globe. After all, Plato's most celebrated image of humanity striving for a glimpse of truth involves shadows cast on the wall of a cave. In Narnia, the shadows speak.
'The Lion, the Witch and the Wardrobe' opens on 8 December