“How does anybody maintain health of mind outside the Church?” asked the famed British author Evelyn Waugh, in the afterglow of his conversion to Catholicism. “It becomes increasingly rare as more chinks appear in the iron curtain of invincible ignorance.”

After an early adulthood devoted to hedonistic pursuits and shadowed by an adulterous first marriage, Waugh credited his newfound faith with aiding a recovery of hope and moral order. The Church also taught him to embrace the writer’s life as a deeply worthy pursuit — not a second-best avocation of the hack who couldn’t cut it in the “real world.” Brideshead Revisited, Waugh’s best-selling 1944 novel recounting the transformative power of divine grace on a disparate group of English aristocrats, testifies to the author’s gratitude for his spiritual awakening.

Yet, anyone who has seen the recently released film adaptation of Brideshead Revisited will be hard put to identify a single mental-health benefit gained by Church membership. Instead, the film presents a Catholicism that crushes human potential and nourishes despair. Indeed, the film subverts the author’s intentions, and in doing so, it reveals our present culture’s hostility for religious dogmas that resist moral relativism and batter the psyche with seemingly impossible demands.

But, the film’s problems can be blamed, in part, on Waugh himself. His astute characterization of an oft-admired but flawed Catholic type — “saintly, but not a saint” — continues to befuddle the devout, even as it encourages the bigotry of non-believers. Brideshead Revisited, you might say, provides a case study for religious fervor run amok. Who can fault a screenwriter for getting the book wrong?

From the beginning, the film version starts off on the wrong foot. Its plot turns on a love triangle — Charles Ryder, the narrator, develops a romantic friendship with Sebastian Flyte — the younger son of Lord and Lady Marchmain, but soon transfers his affections to Julia Flyte, the rebellious older sister.

Lady Marchmain, morally scrupulous in the extreme, has already driven her husband into the arms of a sympathetic mistress. Now, taking note of Charles Ryder’s atheism, she encourages Julia to marry Rex Mottram, the Philistine money man who wants to buy an aristocratic bride. Lady Marchmain’s poor judgment in encouraging Mottram’s suit is only equaled by her obsessive orthodoxy, a poison that stunts the emotional development of her offspring.

Assaults against the psychological burden imposed by Catholic moral teaching are nothing new. But it’s noteworthy that the screenwriter arrives at this position by dramatically altering the original plot and by brutally transforming the character of Lady Marchmain. Both changes are unfortunate, for the author put every element of his novel to good purpose.

In the novel, there is no love triangle, but rather a rough symmetry between Charles Ryder’s formative relationship with Sebastian and his subsequent, full-blown love for Julia. Symmetry, of course, should not be confused with equality. The romantic friendship of two adolescent boys is one thing. The fruitful promise of a man’s love for a woman is of another order.

Sebastian is the “forerunner,” in the narrator’s words. Sebastian unlocks the “enchanted garden” of human transcendence for Charles Ryder, a good pagan whose alienated bachelor father has raised him to anticipate a loveless and pointless existence. The half-ruined faith and beauty he encounters at Brideshead, the glorious pile inhabited by an idiosyncratic Catholic family, introduces the self-described “agnostic” to the joys and sorrows of real love — and to his vocation as an artist.

Thus, Charles Ryder commences his pilgrimage to manhood. Sadly, Sebastian can’t withstand the rigors of this journey. He wishes life could “always be summer.” He turns to drink as a sop for his immaturity and terror. But Lady Marchmain doesn’t move to shore up her son’s confidence. Instead, she assigns him a professorial watchdog and dispatches them on a grand tour. She, literally, cannot bear his imperfections.

When Sebastian departs, Charles enters a period of mourning. Then a chance meeting with Julia Flyte brings Charles back to life. Julia, too, has been mourning her own lost innocence. Rex Mottram — the man she married against her mother’s wishes — is an adulterer and only “half a man” who toys with people, just as he manipulates the financial markets.

Faced with the possibility of loving a woman, Charles comes to understand Sebastian’s special significance: He is “the forerunner” whose friendship prepares Charles to offer himself unconditionally to Julia. But Charles’s reference to “the forerunner” also underscores the deeper significance of the novel’s symmetry.

For Waugh, the history of salvation reveals the mysterious role of those who “make straight the way of the Lord,” just as John the Baptist prepares his people for the true Messiah. Revelation is packed with a rough symmetry, with forerunners preparing the way for what is greater still: the Old and New Testament, Adam and Christ, the new Adam, Eve and the Virgin Mary, the new Eve. The “one-flesh” union of Adam and Eve, and that “mystery hidden since time immemorial” — the Church, the bride of Christ. Charles Ryder’s ignorance of spiritual matters blinds him to the source of all love for whom he is being prepared. He doesn’t know it yet, but Julia, too, is a forerunner.

The filmmaker’s decision to substitute a banal love triangle for the powerful symmetry of Waugh’s conversion story banishes the author’s primary insight: Grace, like the story of salvation, works organically, building on every aspect of human experience: the sacred and the profane, human strength and weakness, joy and suffering, pious mamas and rebellious offspring. In the filmmaker’s mind, Catholic moral teaching, personified in the character of Lady Marchmain, threatens the mental health of believers. But a dulled conscience — where it’s “always summer” — is the only obvious antidote, and that path requires a denial of reality itself.

Waugh doesn’t make it easy for us to see the grace working amidst the confusion and suffering. Sebastian’s collapse into alcoholism is a reprise of his father’s early adulthood. Then, too, Lady Marchmain confronts human weakness and responds with condescension. During most of the novel, Lord Marchmain resides with his mistress in Venice, in exile from his family, church and ancestral responsibilities.

Who is to blame for the plight of the Marchmain men? The power of Brideshead Revisited turns, in part, on the author’s complex treatment of culpability. Lord Marchmain and Sebastian do wrong, but they receive little mercy or encouragement to change their ways. Lady Marchmain is the stronger, and we tend to blame the strong for the missteps of the weak.

But contrary to the film’s caricature of a religious monster, Waugh presents her with great subtlety and even sympathy. Lady Marchmain is elegant, beautiful and ironic. Blind? Yes. She doesn’t see that her way of believing permits no human weakness, though her savior is most at home amid the vulnerable and childlike. And her charm is said to be deadly. A gossip describes her as “sucking the blood” out of her victims —family and courtiers alike.

Waugh’s chilling portrait makes Lady Marchmain an easy target. We can see why the film presents her as exhibit A in the case against Catholicism. But if the screenwriter had delved more deeply into the text, a more nuanced understanding of this character would enrich this adaptation.

“You didn’t like her. I sometimes think that when people want to hate God, they hate Mummy,” Cordelia, the youngest member of the family, tells Charles Ryder. “You see, she was saintly, but she wasn’t a saint. No one could really hate a saint, could they? They can’t hate God, either. When they want to hate him and his saints, they have to find something like themselves and pretend it’s God and hate that.”

Charles Ryder’s hostility toward Lady Marchmain is intertwined with his fear of God and the entanglements of faith. When he moves toward belief, his visceral dislike of Lady Marchmain fades. Her essence is revealed to be nothing more than blind human nature. Yet, she is no more clueless than the narrator himself. The modern man who snorts at the idiocy of incensed rituals, Charles Ryder won’t consider why they unsettle his soul.

Lady Marchmain penetrates Charles’ armor of skepticism, even as she silently bears her maternal cross, ceaselessly praying for her wayward children. The economy of salvation excludes no one. This truth still fuels the novel’s power to astonish and seduce the reader — even those taught to doubt the sanity of the religiously devout.

Joan Frawley Desmond writes for a variety of publications on religious and cultural topics, and lives in Maryland.