This paper analyzes a little-studied aspect of Bishop Alonso de Cartagena (1485–56): that of a theologian embroiled in a polemic dispute with Pero Sarmiento and Marcos García de Mora, organizers of the Toledan anti-converso riots of 1449. In this dispute, Cartagena demonstrates a formidable dialectic force, which he develops in his treatise Defensorium Unitatis Christianae. His theological discourse would become a battleground in which, Bible in hand, he revealed the belligerent, irrational and, at the same time, ideological and heretical nature of his adversaries’ arguments.
Cartagena represents the critical conscience of the conversos of his time and epitomizes an ambitious and valiant Christian humanism in his attempt to save the unity of Christian society from the cultural and social rift the Toledan crisis clearly embodied. His originality lies in having understood the importance of language as a medium and, therefore, the need to neutralize the “virus” inside it: the preconceived and artificial conceptions that the Toledo rebels had of conversos.
Furthermore, his assertion that the papacy should maintain full control of the punishment of heretics led him to suggest repeatedly to John II of Castile that matters of faith did not concern the civil authorities.
His role as a theologian reveals itself in his decisive contribution to the expression of a new religious identity: that of the conversos, who thanks to him, began to familiarize themselves with theological concepts such as justification by faith and works such as the Beneficium Christi, which would later play a role in the Spanish and European religious crisis of the sixteenth century.