In 1998 I went to the University of Mississippi, in Oxford, to become a writer-in-residence. I was working on Great Disappointment, a historical novel about my great-grandfather William Miller, whose religious movement was the forerunner of the Seventh-Day Adventist Church. Miller, using Bible math, determined that Jesus would be coming down on October 22, 1843. I had read Miller’s letters and gone to see the cracked painted canvases of winged lions and fiery angels that adorned the hall where his prayer meetings were held. But I couldn’t get my head around his blind faith, and as a consequence Great Disappointment had stalled out. I didn’t want to treat Miller like a lunatic. Before I could continue I needed to understand Miller’s theology and find a way to respect his beliefs.

I stopped writing for a few weeks. My two-year-old daughter and I spent a lot of time across the street on the grounds of William Faulkner’s dilapidated mansion. We’d go over at twilight, when the big white house had a patina like the inside of a shell, and chase fireflies among the cypress trees and boxwood hedges. On many fronts I felt like a failure. My novel was stalled, and I was estranged from my husband. I’d been awarded this prestigious fellowship, endowed by John Grisham, and yet I wasn’t able to write.

I realized that before I could continue with Great Disappointment, I would have to develop some spiritual muscles—not necessarily a faith in the physical coming of Christ (that may always be beyond me), but an actual sustaining practice, a theology I could live within. With most of my characters I catapult myself into their minds and can therefore construct a believable psychology. But with Miller, my secular imagination wasn’t enough. I admired Miller’s religious conviction, however outsized, and I needed to create this for myself, wanted to believe in something that was glorious and impossible. This desire was not entirely new: since the birth of my daughter questions of faith had haunted me. Giving birth had been traumatic and spectacular and had left me with a hint of life’s grandeur, meaning, and texture, but it felt as if there was no place for these feelings to unfurl or manifest. In the months after giving birth, I had begun to go to noon mass at the local Catholic church near where I lived in Brooklyn. I am a Lutheran minister’s daughter, so I felt comforted by the familiar vaulted ceilings and the candles burning all around in red glass holders. I liked that people around me—secretaries, janitors, businessmen and businesswomen in dark suits—were spending their lunch hours in prayer. I’d sit among them with my baby sleeping, her tiny face pressed against the side of the carrier.

The only problem was that the priest delivered the liturgy in a monotone. His voice was always at the same numbing, droning pitch. I wanted to talk to somebody about God, and sometimes I’d imagine meeting with the priest in his dark office beyond the sacristy. But the man seemed spiritually despondent, and I couldn’t fathom that a conversation with him would do me any good. In Oxford, while I didn’t attend church, I was still longing for God. I read The Cloud of Unknowing, a mystical guide to prayer written in the 14th century, which I had bought from the gift shop at Holy Cross Monastery the summer before. I identified with the anonymous writer’s sense of isolation and the practical advice to imagine oneself before a great cloud God swirling somewhere mysteriously inside. I knew the Lord’s Prayer and Now I Lay Me Down to Sleep, the prayer I had said as a child. But the prayer described in The Cloud of Unknowing was three-dimensional, more like space travel then rote repetition.

Up until that year, my most developed internal incantations had to do with fantasizing about sex. Maybe because of this, my first attempts to pray resembled scenes from a Victorian bordello. My cloud was purple, like the purple smoke I’d once seen at a Prince concert, and I imagined myself lying in front of the swirling mass in a green velvet gown. I rested there on a warm blanket and was comforted by the idea that, though hidden in vapor, I was in the presence of God. My amateur practice comforted me, and sporadically I did feel a divine presence, but I wasn’t yet ready to go back to Great Disappointment. I wanted to start writing again, and I decided that while waiting for the development of my faith, I’d write an erotic novel.

I began in my attic office, and a draft came quickly, an odd, overly lyrical draft clearly influenced by the atmosphere of my fledgling attempts to pray. I threw the draft away and began again. I spent months on the first 40-page section only to find it in the rewriting process evaporating down to four.

Disappearing pages wasn’t the only surprise as I worked on this novel, which I called Milk. Characters who were supposed to care exclusively about each other began to discourse on God. Sexual longing, I began to realize, was just another facet of religious longing. I joked with friends that my new book would be a cross between The Story of O and St. John of the Cross’s Dark Night of the Soul.

Milk’s main character Mary is a new mother transformed by the birth of her baby. As her baby sleeps in his crib, she can never decide if she should kneel in her coat closet and pray or fantasize about sex. For Mary, the gory beauty of birth is both spiritually radicalizing and mentally destabilizing, and she finds herself vulnerable to visions and paranoia. Mary is new to the spiritual life and disoriented by the process of passing from the known to the unknown. Spirituality, she finds, is much like technology in that once a phase is perfected it nullifies itself and a new phase begins. Milk’s structure is based on the religious triptych, with Mary on the large middle panel; John, a former monk searching for God’s love in the secular world of intimacy, on the left; and Mary’s friend Walter, a gay Episcopal priest, on the right. Walter struggles with his lonely life as a parish minister and against his attraction to teenage boys. In my novel, every character has his or her own theology no matter how rudimentary or off-center, and these theologies relate mysteriously and, I believe, subtly, to one another, much like the components of the Trinity.

I often think of a segment I saw on 60 Minutes that featured the new-age guru Marianne Williamson. She was speaking in front of a huge group of women in Los Angeles, and as the sound bite came in she was saying, “When you call out during sex, ’Oh, God,’ it’s because he is there.” All the women jumped out of their seats and cheered. I was somewhat shocked that this simple message, that God is incarnate in sex, was so moving to these women.

In our culture there is a sense that sex is without God, that God forsakes, that this single activity in life is not infused with God’s presence. This may be why readers are so uncomfortable with sex scenes in literary novels. Last October Walter Kirn wrote in The New York Times Book Review that sex scenes in fiction are “a problem”: “Whether they’re rendered crudely and directly, through graphic close-ups and blunt four-letter words, or delivered elegantly and obliquely, through misty impressions and lofty euphemisms, most displays of literary lovemaking tend to make the reader’s flesh crawl.” It’s odd, the unexamined quality of Kirn’s observation. Why should sex, an act so fundamental to the emotional lives of human beings, be considered generally repugnant? Sex in our culture is like a piece of soiled fabric cut from a greater garment. Maybe this dichotomy (sex vs. everything else) is unavoidable, part and parcel of original sin, but I think that sex, even at its most sordid, is soaked through with both humanity and divinity. During the writing of Milk I began to sense that grace flows through the world evenly and that there is no patch of life or set of actions outside the divine’s domain.