The traditional account of the development of theology in the twelfth and thirteenth centuries is that the emerging “academic” discipline of theology was separated from the Bible and its commentary, that the two existed on parallel but separate courses, and that the one developed in a “systematic” direction whereas the other continued to exist as a separate “practical” or “biblical-moral” school. Focusing largely on texts of an allegedly “theoretical” nature, this view misunderstands or, indeed, entirely overlooks the evidence issuing from lectures on the Bible — postills, glosses, and commentaries — notably the biblical Glossa “ordinaria.” A witness to an alternative understanding, Peter Comestor, master and chancellor of the cathedral school of Paris in the second half of the twelfth century, shows that theology was created as much from the continued study of the Bible as from any “systematic” treatise. Best known for his Historia scholastica, a combined explanation and rewrite of the Bible focusing on the historical and literal aspects of sacred history, Comestor used the Gloss as a textbook in his lectures on the Gospels both to elucidate matters of exegesis and to help him deduce doctrinal truth. Through a close reading of Comestor's lectures on the Gospel of John, this essay reevaluates the teaching of theology at the cathedral school of Paris in the twelfth century and argues that the Bible and its Gloss stood at the heart of this development.