The daughter of a Lutheran pastor and a distant relative of one of the founders of the Seventh-Day Adventist Church, Darcey Steinke has an intimate relationship with “Pentecostal hysteria,” as she puts it. In her fourth novel, Milk, she creates her own brand of Christianity, obsessively physical: Sex becomes a florid, religious event. For the un-virginal heroine, Mary, the orgasm is a “little God,” involving butterflies, baby lambs, and “icy teaspoons” of dirt.

A postpartum-crazed “spooky chick,” Mary is so consumed by her newborn son that milk (“the Great Beyond”) perpetually drips from her nipples. Wavering between spiritual enlightenment and total lunacy, she prays in random coat closets, her voice muffled by cashmere, her knees pressed against extra rolls of toilet paper. When her hipster husband gets fed up with the “God stuff,” she starts sleeping with a former monk, having wild sex (in a nursing bra) while thinking about whether or not the baby is hungry.

Bristling with references to the Virgin Mary as “porn star,” Milk reads like a perverse Bible fable, unified by the idea that the church holds “the same cozy qualities as your bedroom.” In her afterword to Joyful Noise, a collection of essays about religion, Steinke writes that “our physical connection to our mothers . . . raises the hair on our collective necks.” In this jarring wisp of a novel, she probes the possibilities of that first bond, both erotic and otherworldly.