This paper concerns a passage in a lost work by Diego de Valera in defence of conversos, dedicated to Lope de Barrientos, bishop of Cuenca, and against a friar who preached in that town, where the author was born and lived at that moment (1458). We analyse both the specific circumstances that led to the composition of the text, which are linked with Mosen Diego's biography and the local political situation, and its ideological and literary aspects, especially its relation to the rest of Valera's works. [ABSTRACT FROM AUTHOR]