THE PEQUEA CREEK scrawls a looping signature through the farmland east of the city of Lancaster, Pennsyl­vania. On a map, one can see the creek’s cursive script winding between Route 30 and Route 340, two of the major routes through Amish country. Eleven million tourists visit Lancaster County each year, many of them traveling Route 30, with its chain restaurants, mega-outlets, and mini-golf courses, and Route 340, flanked by billboards for Jakey’s Amish Barbeque, Amish Country Aerial Tours, and Abe’s Buggy Rides.

Near one oxbow of the Pequea, and not far from these highways, sits the Gordonville Book Store. Owned by an Amish man, the bookstore is a modest building with beige siding. On this snow-covered January day, laundry hangs stiff as card stock on the line between the store and an adjacent house. The store, which sells books, calendars, greeting cards, and gifts, serves mostly Amish and conservative Mennonite patrons. Sometimes English (i.e. non-Amish) people like me happen upon the store, and are pleased to find gas lanterns humming sotto voce and an Amish boy with a bowl cut and a high voice manning the cash register.

On the pavement a few feet from the front door sits a stack of neatly taped boxes apparently delivered that morning. The words “Thomas Nelson” and the company’s logo, a house, are emblazoned on the sides. At the time of my visit, Thomas Nelson is one of the largest Christian publishers in the world. A little over a year later, it will be bought by HarperCollins, a subsidiary of Rupert Murdoch’s News Corp.

I do not know what books these boxes hold, but as I step inside the door, a shelf to my left offers a clue: Amish romance novels, all with covers depicting lovely Amish-clad Mädchen hovering over pastoral landscapes, line the shelves. A handwritten note on neon green paper taped to one shelf says, “New! Lydia’s Charm.” Published by Barbour Books, the novel tells the gentle story of a widow who moves to Charm, Ohio, and is pursued by two Amish suitors, one a widower with three unruly boys and the other a shy bachelor. Lydia’s Charm is joined by Amish novels published by Thomas Nelson, Zondervan, Bethany House, Revell, Harvest House, and other evangelical houses.

Most of these books, I discovered, were in fact written not by Amish authors but by evangelical Christians. On the Venn diagram of American religion, evangelical and Amish circles share some space. But while they have some aspects in common — a commitment to traditional Christian theology, a high view of Scripture, the conviction that faith should matter in daily life — evangelicals and the Amish are largely separate tribes, speaking distinct cultural dialects that are at times mutually unintelligible. Evangelical Christians themselves come in at least fifty shades, from politically and socially conservative fundamentalists to theologically progressive environmental activists, but most emphasize a personal experience of conversion, relevant witness to the surrounding culture, and the critical nature of evangelism. Evangelical writers of Amish romance novels channel these convictions in their books, with a typical Amish heroine traveling two vectors as her story unfolds: one from the works-based religion of her people to a more warm-hearted and evangelical spirituality, and another from loneliness to love.

The Ami...