Christology and ecclesiology, both vital to Flannery O'Connor's thought, are reflected principally in her book reviews, letters, and essays. The reviews in particular (69 of the 143 titles reviewed pertain to subject matter that is religious or theological) attest to the range, depth, and vitality of her own theological investigation. By 1961, O'Connor's theology had been substantially influenced by that of Karl Adam, Romano Guardini, Pierre Teilhard de Chardin, and Francis Durrwell. Through the influence of these theologians, one can trace in O'Connor's nonfiction the development of her Christology and its impact on her fiction.