One day in 370 C.E., a sixteen-year-old boy and his father went to the public baths together in the provincial city of Thagaste, in what is now Algeria. At some point during their visit, the father may have glimpsed that the boy had an involuntary erection, or simply remarked on his recently sprouted pubic hair. Hardly a world-historical event, but the boy was named Augustine, and he went on to shape Christian theology for both Roman Catholics and Protestants, to explore the hidden recesses of the inner life, and to bequeath to all of us the conviction that there is something fundamentally damaged about the entire human species. There has probably been no more important Western thinker in the past fifteen hundred years.

In the “Confessions,” written around 397, Augustine described what happened in the bathhouse many years earlier. That day, Patricius, his father, saw in him the signs of inquieta adulescentia, restless young manhood, and was—in Sarah Ruden’s new, strikingly colloquial translation—“over the moon” at the thought of someday soon having grandchildren. It is easy, even across a vast distance in time, to conjure up a teen-ager’s exquisite embarrassment. But what fixed itself in Augustine’s memory, instead, is something that happened when they got home: “In his glee he told my mother—it was the sort of tipsy glee in which this sorry world has forgotten you, its creator, and fallen in love instead with something you’ve created.” (Augustine’s “Confessions” are addressed to his God.) His mother, Monica, was a pious Christian and responded very differently. Since God had already started to build his temple in her breast, she “endured a violent spasm of reverent, tremulous trepidation.” The unbaptized adolescent’s sexual maturity had become the occasion—not the first and certainly not the last—for a serious rift between his parents.

Patricius did not concern himself with his son’s spiritual development in the light of Jesus, nor did he regard the evidence of his son’s virility with anything but delight. In response, Monica set out to drive a wedge between son and father. “She made a considerable bustle,” Augustine writes, admiringly, “to ensure that you, my God, were my father, rather than him.”

About one thing the father and mother agreed: their brilliant son should obtain the education his gifts deserved. The young Augustine had been sent to study in the pleasant town of Madauros and had shown remarkable facility in literary interpretation and performance. The university at Carthage seemed within reach—followed, possibly, by a lucrative career in law or public speaking. Patricius, a man of modest means, scrimped and networked for a year to collect the needed funds. When Augustine left Thagaste, he must have seen his father for the last time, for in the “Confessions” he mentions that when he was seventeen Patricius died. The mention is a conspicuously cool one.

If the grieving widow also felt some relief at his death—given that he was a dangerous influence on her beloved son—any hopes she might have had that Augustine would embark at once on the path of chastity were quickly dashed. “I came to Carthage,” he writes, “to the center of a skillet where outrageous love affairs hissed all around me.” His confession that he polluted “the shared channel of friendship with putrid rutting” sounds like an overheated account of masturbation or homosexuality; other, equally intense and equally cryptic phrases evoke a succession of unhappy affairs with women. The feverish promiscuity, if that is what it was, resolved fairly quickly into something quite stable. Within a year or two, Augustine had settled down with a woman with whom he lived and to whom, in his account, he was faithful for the next fourteen years.

The arrangement was probably the best that Monica could have envisaged at this stage for her son, given his restless sexual energies. What she most feared was a hasty marriage that might hinder his career. Merely living with a woman posed much less of a threat, even when the woman gave birth to a son, Adeodatus. By the standards of the time, the relationship was a respectable one. At least from Augustine’s perspective—and that is the only perspective we have—there was no thought of his marrying the woman, whose name he does not even bother to provide. He expects his readers to understand the difference “between the sanctioned scope of marriage, a bond contracted for the purpose of producing children, and a deal arising from lustful infatuation.”

Priding himself on his intelligence and his literary sensitivity, he studied law; he honed his rhetorical skills; he entered dramatic competitions; he consulted astrologers; he mastered the complex, sinuous system of thought associated with the Persian cult known as Manichaeanism. Augustine carried his Manichaeanism, along with his mistress and his son, from Carthage to Thagaste, where he taught literature, and then back to Carthage, where he gave courses on public speaking, and then to Milan, where he took up an illustrious professorship of rhetoric.

In Augustine’s decade-long ascent, there was one major problem, and her name was Monica. When he arrived at Thagaste for his first teaching position, Augustine’s mother was loath to share a house with him, not because of his mistress and child but, rather, because of his Manichaean beliefs. Those beliefs—the conviction that there were two forces, one good and the other evil, at war in the universe—were repugnant to her, and she made a conspicuous show of weeping bitterly, as if her son had died.

Her tears were redoubled when, back at Carthage, he prepared to leave for Rome: “She was hanging onto me coercively, trying to either stop my journey or come along with me on it.” Lying, he told her that he was only seeing off a friend, and persuaded her to spend the night at a shrine near the harbor. “I got away, and got away with it.”

The son must have felt some guilt. And yet, in remembering this moment, he allowed himself for once to express some anger toward his mother: “Her longing, which was physical, was taking a beating from the justified whip of sorrow.” The phrase Augustine uses for this longing—carnale desiderium—might seem more appropriate for a lover than for a mother. Monica had taken whatever was blocked or unsatisfied in her relationship with her husband and transferred it to her son. Augustine, suffocating, had to flee. And the suffering that his escape visited upon her was, he reflects, her due as a woman: “these tortures revealed the vestiges of Eve she had within her, as with groans she searched for what she had given birth to with groans.”

In Genesis, the consequence of Eve’s disobedience is twofold: women are condemned to bring forth children in pain and to yearn for the husbands who dominate them. As Augustine looks back at his relation to his mother, child and husband are merged in him: she brought him with sorrow into the world and she sought him with sorrow through the world. For his grieving mother’s search for her son did not end at the harbor in Carthage. A few years later, when Augustine took up his post in Milan, Monica sailed from North Africa to join him.

This time, he did not flee. Though he was not ready to be baptized a Catholic, he told his mother that he had been deeply impressed by Ambrose, the Catholic bishop of Milan. Ambrose’s powerful sermons helped to undermine Augustine’s contempt for the apparent crudeness of the Bible’s stories. What had originally struck him as absurdities began to seem like profound mysteries. His long-held intellectual and aesthetic certainties were crumbling.

All the while, Augustine’s career continued on its course. He met his students in the morning, and spent his afternoons with his close friends, discussing philosophy. His mother, now settled in his household, sought to change her son’s life. She busied herself with arranging a favorable marriage, and found a suitable Catholic heiress whose parents agreed to the match. The girl was almost two years shy of marriageable age, though, and so the wedding had to wait.

In the meantime, Monica engineered another change in her son’s life. The woman with whom he had been living “was torn from my side, because she was supposed to be an obstacle to my marriage,” Augustine writes. “My heart, which had fused with hers, was mutilated by the wound, and I limped along trailing blood.” Of his mistress’s feelings, he gives us no glimpse, noting simply, “She went back to Africa, vowing to you that she would never know another man.” Then she is gone from his account, leaving him with the gnawing sexual appetite that she had served to appease. He quickly took another mistress.

Yet, as he soon came to testify, God’s grace works in strange ways. In little more than a year’s time, Augustine had converted to the Catholic faith. Shortly thereafter, now baptized, he broke off his engagement to marry, resigned his professorship, vowed himself to perpetual chastity, and determined to return to Africa and found a monastic community. By running away from his mother, he had, without realizing it, embarked on a spiritual journey that would surpass her utmost dreams.

Characteristically, he was able to embrace Lady Continence, as he put it, only in the context of a much larger rethinking of the nature of sexuality. He needed to understand the peculiar intensity of arousal, compulsive urgency, pleasure, and pain that characterizes the human fulfillment of desire. He was not looking back on these feelings from the safe perch of a diminished libido, or deluding himself that they were abnormal. As a young man who had already fathered a child, he knew that, for the entire human species, reproduction entailed precisely the sexual intercourse that he was bent on renouncing. How could the highest Christian religious vocation reject something so obviously natural? In the course of answering this question, Augustine came to articulate a profoundly influential and still controversial vision of sexuality, one that he reached not only by plumbing his deepest experiences but also by projecting himself back into the remotest human past.

In the Roman port of Ostia, a few days before setting sail for Africa, Augustine and his mother were standing by a window that looked out onto an enclosed garden, and talking intimately. Their conversation, serene and joyful, led them to the conclusion that no bodily pleasure, no matter how great, could ever match the happiness of the saints. And then, “stretching upward with a more fiery emotion,” Augustine and Monica experienced something remarkable: they felt themselves climbing higher and higher, through all the degrees of matter and through the heavenly spheres and, higher still, to the region of their own souls and up toward the eternity that lies beyond time itself. And “while we were speaking and panting for it, with a thrust that required all the heart’s strength, we brushed against it slightly.”

It is difficult to convey in translation the power of the account, and of what it meant for the thirty-two-year-old son and the fifty-five-year-old mother to reach this climax together. Then it was over: suspiravimus. “We sighed,” Augustine writes, and returned to the sound of their speech.

The moment of ecstasy that Augustine and his mother shared was the most intense experience in his life—perhaps, as Rebecca West remarked, “the most intense experience ever commemorated.” A few days later, Monica fell ill, and died soon after. The “Confessions” does not take the story of Augustine’s life further. Instead, it turns to a philosophical meditation on memory and an interpretation of the opening of Genesis, as if that were where his whole autobiography had been heading. Why Genesis? And why, in the years that followed, did his attention come to focus particularly on the story of Adam and Eve?