This dissertation addresses an essential component of the Christianization of the Roman Empire, the catechetical sermons used by clergy to train those converting to Christianity. This genre of homilies reached its most developed expression towards the end of the fourth century as subjects of the Roman Empire converted in increasing numbers. As much of the recent scholarship on Christianization has focused on institutional or demographic models, catechesis has received insufficient attention. Focusing attention on catechesis creates room for the study of Christianization which is sensitive to both the episcopal program for conversion and the popular appropriation of that program.

Theodore of Mopsuestia delivered his catechetical homilies during the early 390s while he was a priest in Antioch. This study begins by looking at the variety of rhetorical approaches to catechesis within that context. It analyzes the ecclesiastical setting of Antioch and considers the self-presentation of the community to which people were converting. The ecclesiology propagated in Antioch suggests a rigid hierarchy with the bishop at the top, followed by the priests, deacons, lower clergy, and finally the laity. This ecclesiastical structure provided a cohesive framework for the incorporation of converts into the Christian community.

Theodore carefully crafted these sermons in order to guide the catechumens through the intricacies of Christian belief and practice. He gave considerable attention to employing established Christian metaphors and fashioning entirely new ones in the cultivation of a uniquely Christian imagination. He used intricate imagery to train his pupils theologically, while also giving them detailed descriptions and interpretations of cultic activities such as baptism and the eucharist. The whole curriculum presented a carefully crafted Christian symbolic worldview through which Theodore invited converts to engage themselves in the orthodox beliefs and practices of the community.

Considering Christianization through the lens of catechesis opens new ways to understand complicated social, religious, and political phenomena. Highlighting the communal, intellectual, cultic, and imaginative components of catechesis adds nuance and texture to the study of the Christianization of the empire. It allows for a deeper understanding of mixed motives in individual converts and the ostensible Christianization of institutions.