John W. Nevin was the driving force behind the Mercersburg Theology, which Sydney Ahlstrom's A Religious History of the American People notably described as "the outstanding example of the Catholic tendency in American Protestantism." The Mercersburg Theology took its name from the Pennsylvania village where Nevin taught at the seminary of the German Reformed Church from 1840 to 1851. This dissertation examines the Mercersburg Theology as Nevin's attempt to address what he perceived to be a crisis of epochal proportions. Throughout Nevin's Mercersburg writings one finds references to the "church question" as the all-encompassing problem of the day. For Nevin, the church question was not merely an attempt to assess the rival doctrinal claims of competing denominations. Rather, he urged his contemporaries to consider that the conditions for the possibility of fully Christian existence simply did not exist within the strictures of mainstream American Christianity. In short, the critical thrust of the Mercersburg Theology was to convict antebellum American Protestantism that it suffered from a lack of catholicity. In the early 1850s, after nearly a decade of prolific, creative, and controversial scholarship, Nevin resigned his professional posts, giving rise to rumors that he would soon become a Roman Catholic. In the end, he did not convert, but Nevin -- and the Mercersburg Theology itself, with its grand hopes for an Evangelical Catholic church of the future -- had clearly reached an impasse. In this contextual, diachronic reading of Nevin's classic Mercersburg writings, I argue that the Mercersburg Theology is most instructive for contemporary reflection on the ongoing Catholic tendency in American Protestantism more generally precisely at the point at which Nevin tried-and failed-to resolve the church question to his own satisfaction. I contend that there is a correlation between Nevin's inability to bring the church question to a resolution and his equally inconclusive consideration, during these same years, of the classic scholastic inquiry into the motive for the Incarnation. This is a crucial link, since Nevin insisted upon a determinant relationship between the church question and the "Christ question" (i.e., Christology). Since he refrained from settling the question of whether God would have entered human history had humanity never sinned, Nevin seems to have acknowledged that insufficiently disciplined Christological speculation threatens to reduce the ultimate mystery at the heart of Christian faith. In the same way, his failure to resolve the church question suggests that Nevin ultimately believed that to provide a clear and distinct account of "historical development" (or its absence), upon which the Reformation, and the far-reaching effects variously attributed to it, can be justified as necessary (or, conversely, categorically dismissed) remove the Incarnation from what he insisted was its rightful place as the cardinal fact of history. The unfinished character of Nevin's quest serves as a kind of parable for the "Catholic tendency in American Protestantism," which indicates why the church question continues to be raised, and suggests why its resolution continues to remain elusive.