The doctrine of divine providence was considered fundamental to understanding the nature of reality in medieval Christian orthodoxy. One of our greatest modern impediments to proper understanding of this law are the radically different ontologies that flourished in the Latin West through the recuperation of Ancient thought, most notably in the divisions between the Platonists and the Aristotelians. Whereas Biblical exegesis owed more to Augustine's Platonism, the rise of Aristotelian thought in the university curriculum entailed a serious threat to the doctrine of providence. The translation and dissemination of Islamic Aristotelians revealed an almost identical challenge to Islamic orthodoxy on the same matter. Philosophical, and especially ontological, speculation on the nature of substance (ontology) was therefore fertile ground for heresy. The main works under examination are the anonymous Queste del Saint Graal and the continuation of the Roman de la Rose by Jean de Meun. Deeply imbued with Augustinian figuralism and Biblical history, the Queste strongly distinguishes itself from the rest of the Lancelot en Prose, most notably La Mort le Roi Artu, in its theological purpose. It also shows a clever reworking of its source materials (Chrétien de Troyes and continuators, Robert de Boron, Perlesvaus) and an attempt to re-write the grail literature in its most sophisticated and orthodox formulation. By contrast, Jean de Meun's Rose continuation is fraught with heresy and obscenity as he denounces the corrupt practices of the mendicant orders and marks his clear preference for the University of Paris's secular masters (ca. 1270). Analyzing the question of ontology within the work, one notices heresies that originate in the Islamic reception of Aristotle, and which resulted in the large-scale condemnations within the decade of the continuation's composition. While strikingly different in tone and purpose, the Queste and the Rose are theological romances that use the concept of providence to explain the special place of man. While the former offers an explanation based on church sacramental practices, the latter offers an extreme naturalism with an Arab-inflected Boethius as its principal source.