The puzzle of a small sect’s against-all-odds triumph fascinates Carrère. Illustration by Nick Little

Kierkegaard relates a chilling parable in “The Sickness Unto Death.” An emperor summons a poor day laborer. The man never dreamed that the emperor even knew of his existence. The emperor tells him that he wants to have him as his son-in-law, a bizarre announcement that must strike the man as something he would never dare tell the world, for fear of being mocked; it seems as if the emperor wanted only to make a fool of his subject. Now, Kierkegaard says, suppose that this event was never made a public fact; no evidence exists that the emperor ever summoned the laborer, so that his only recourse would be blind faith. How many would have the courage to believe? Christ’s kingdom is like that, Kierkegaard says.

The French writer Emmanuel Carrère doesn’t mention Kierkegaard in his latest book, “The Kingdom” (Farrar, Straus & Giroux), but the Danish philosopher—the Danish Christian lunatic, one might say—hovers over the book as God’s face is said to have hovered over the waters during the creation of the world. The Kierkegaard whose work is scarred by the great “offense” of Christianity, by its shocking challenge to reason and empirical evidence; who claimed that modern philosophy amounts to the premise “I think therefore I am,” while Christianity equals the premise “I believe therefore I am”; who writes that the best proof that God exists is the circular proof one was offered as a child (“It is absolutely true, because my father told me so”)—that brilliant, mutilated Christian is the unnamed patron of “The Kingdom.” An amazingly various book, it narrates the author’s crises of religious faith in the nineteen-nineties; combines conventional history and speculative reconstruction to describe the rise of early Christianity; deftly animates the first-century lives and journeys of Paul, Luke, and John; and attempts to explain how an unlikely cult, formed around the death and resurrection of an ascetic lyrical revolutionary, grew into the established Church we know today. “Can one believe that such things are still believed?” Nietzsche asked, scornfully. “And yet they are still believed,” Carrère replies.

Fortunately, Emmanuel Carrère lacks Kierkegaard’s anguished Northern masochism. In matters of appetite, he is pleasingly French: sensuous, libidinous—the healthy lover of pagan Mediterranean pleasures that Nietzsche admired and Camus incarnated. He is French in another way, too: he likes reason, argument, evidence, and the virtues of the secular state. Carrère was born in 1957 into a privileged and intellectual family. (His mother, Hélène Carrère d’Encausse, is a distinguished historian and the permanent secretary of the Académie Française.) Though Carrère’s wife jokingly suspects him of being “Catholic around the edges,” he comes from a milieu that was likely to be interested in theology only, in Borges’s words, “as a branch of fantastic literature.”

Yet by the late nineteen-eighties, after launching a fairly successful literary career—a book about Werner Herzog; a few well-received novels—he had become depressed and unproductive: “I could no longer write, I didn’t know how to love, I knew I wasn’t particularly likable. Just being me became literally unbearable.” Influenced by his eccentric godmother Jacqueline, who was a mystic, a poet, and, above all, a devout Catholic, he read Augustine’s “Confessions” and the Gospel of John. That gospel spoke to him so powerfully that he began to read a daily extract and write commentary on it. Broken, vulnerable, and stripped of his intellectual pride, he “became accessible to my Lord.”

It was a fairly short fever. Nowadays an agnostic, Carrère spends the early sections of this book reviewing his almost three years as a committed Christian. What shocks him is the extremism of his faith. He was drawn to theological stringency, melodramatic all-or-nothings, and obnoxiously proud circularity. He is appalled to find in his old notebooks such remarks as this: “The sole argument that can allow us to admit that Jesus is the truth and life is that He says it, and since He is truth and life, He must be believed.” And this: “An atheist believes that God does not exist. A believer knows that God exists. One has an opinion, the other knowledge.”

Carrère has become celebrated for his propulsive, original, free-ranging narratives, which frequently mix memoir, biography, and fiction in rather blithely measured proportions. “I Am Alive and You Are Dead,” his fantastically engaging book about Philip K. Dick, published in 1993, tells the life of the science-fiction writer from within, as if he were writing a novelization of Dick’s life. (Carrère calls him Phil throughout.) There are no references and very few named sources, yet the material appears to rely on the established record, and is clearly built from the same archival labor that a conventional biographer would perform. The same goes for Carrère’s previous book, “Limonov” (2011), which describes the rebellious life and career of the Russian writer and troublemaker Eduard Limonov, who lived in poverty in New York, prospered in Paris, and returned to Russia, where, once an opposition leader, he has since become a fierce supporter of Vladimir Putin. “Limonov” vibrates with borrowed energy: Carrère uses, essentially, a present-tense version of the novelist’s best friend, free indirect style, to inhabit and animate the violently short-circuiting mind of his perpetually unappeased protagonist. It is a hard book to put down, perhaps because it has a certain uneasy moral short-circuiting of its own: again, there are no references, so fact and fiction are allowed to trade uniform and mufti; and Carrère’s pumped-up admiration of Limonov’s often cruel escapades seems, at times, like the wan intellectual’s envy of bloody warfare. (Masha Gessen, in The New York Review of Books, noted numerous errors of fact.)

Carrère works himself and his own stories into these books, partly because he is a good postmodernist, who is suspicious of concealed or “invisible” third-person narrators. He likes intervening frames. As he puts it in “The Kingdom,” “When I’m being told a story, I like to know who’s telling it. That’s why I like narratives in the first person, that’s why I write in the first person and would even be incapable of writing anything differently.” It’s a laudable intention, except that it is almost contradicted by his habit of inhabiting the minds of his biographical subjects. But Carrère is also easy to forgive, because he is such engrossing and charming company—witty, restless, intellectually bold, confessional, shame-proof, simultaneously shallow and deep.

That appeal is powerful in “The Kingdom,” and the tension between first- and third-person narration is better resolved than in his earlier work. Here Carrère’s autobiographical interventions seem not showy or superfluous (as they can in “Limonov”) but necessary. For one thing, it has become exceedingly rare to encounter crises of faith as experienced by a secular intellectual, and Carrère’s oscillation between orthodox fervor and wistful agnosticism holds undeniable fascination. Instead of surreptitiously fictionalizing his story of the rise of early Christianity, he proceeds like a freelance—and slightly offbeat—scholar. His inquiry into the lives and testimonies of Paul and Luke, and their journeys through the far-flung extremities of the Roman Empire, is scrupulously thorough, and relies on an enormous amount of reading, gently summoned. But because Carrère is not a Biblical scholar, and doesn’t want to be one, he allows his imagination to linger and play. He likes to psychologize, to reconstruct scenes and episodes, to speculate when the historical record is thin. Still, he tells us when he’s doing this, and the lack of historical evidence turns out to be his ally, encouraging him to speculate obviously rather than to novelize silently. (There is good French precedent for this kind of intervention: he often cites the nineteenth-century scholar Ernest Renan, whose biographical narrative, “Vie de Jésus,” dared to fill in Jesus’ “lost years,” between his youth and the start of his ministry. In fact, Carrère is much more cautious than Renan, who thickly painted a lyrical portrait of Jesus as a beautiful utopian dreamer.)