«Tolerance against intolerance, freedom against guardianship, humanism against fanaticism, individualism against mechanization, conscience against violence… All these names express an option that ultimately is the most personal and the most intimate, the one that for every individual it is of greater importance: the human or the political, ethics or reason, the individual or the community. " With these words, Stefan Zweig seals one of his most suggestive and disturbing books, Castellio vs. Calvino, a historical review of a controversy that transcends the circumstances of an era - those of a sixteenth century dominated by theological tensions and abuses of power that crystallize in the murder. Servetus - to become the approach to a generic and constitutively human question: the defense of spiritual freedom against violence exercised by power.