This article analyses the little-studied thirteenth-century Arabic inscriptions of the monastery of Santa María la Real de Las Huelgas in Burgos, Spain. Despite their creation during an intensifying Christian–Muslim conflict, they were part of a decorative programme that relied on shared religious ideas and iconography. Their incorporation reinforced daily, funerary and commemorative monastic liturgies. While the article explores the Islamic provenance of these inscriptions, it also reveals the overlooked Arabic New Testament as a source. The inscriptions’ provenance, however, was deliberately obscured first and foremost by the nature of their visual display. Examining the relationship of the Latin to the Arabic inscriptions illustrates an unusual symbiosis between the meaning of the inscriptions, the iconography and the monastery's ritual. This symbiosis was formulated through a highly selective editorial process on the part of the Christian patrons, and predicated on their knowledge of the finer points of Islamic doctrine and cultural practices.