This essay analyzes how late antique commentators on Paul's epistle to the Galatians used the issue of theological disobedience to elaborate the precise meaning of Christian kinship and community in their own times. Paul's anger and frustration at the Galatians, in particular, provided a convenient rhetorical platform for theorizing the nature of and impediments to Christian community in late antiquity. While most Pauline exegetes of the fourth and fifth centuries read the Galatians’ disobedience as a conscious choice born of ignorance, misunderstanding, and weak-mindedness, Jerome located the source of this indiscipline in the Galatians’ ethnic or national disposition. For him, the Galatians were an ethno-theological object—a template upon which he could propose a correlation between Christian error or heresy, on the one hand, and ethnic disposition, on the other. The differences and factions that Paul described in his letters were reimagined in late antiquity as both exemplars of Christian heresy and as heresies of ethnological origin. Ultimately, however, the process of transforming Paul into a heresiologist served only to emphasize the complexity of interpretive maneuvers deployed to define the terms of Christian community vis-à-vis other types of social, political, and ethnic affiliation.