The tolerance controversy against John Calvin
A first appeal of Castellio for religious tolerance is found in his to Eduard the VI directed preface to the Latin translation of the Bible (1551). Probably against the background of the interim that threatened Protestantism in Germany and religious persecution in Italy and France at that time, he denies the secular authority the right to judge over matters of faith, and calls for tolerance and charity, by referring to the New Testament.
Castellio became famous for the “Case of Servet”. In August 1553, Calvin had the Spaniard Michel Servet been arrested while attending church service in Geneva. Servet was burnt alive because of his criticism of the traditional doctrine of Trinity. Already the news of the arrest provoked violent indignation in the humanist circle in Basle: “This event has shocked many pious people and initiated the scandal of scandals, which will hardly ever be forgotten”, as it is stated in the “Report on the death of Servet” (“Historia de morte Serveti”), as its author Castellio applies. The scripture explains why the horror was so tremendous: because Servet was killed cruelly due to his religion and Calvin's help; because the Protestants had allied themselves with the Catholics; because Calvin had the books of Servet burnt; because faith must be free.
Castellio was the spokesman for this criticism, which was more widespread than previously assumed. It manifests itself in verbal utterances, in letters and poems; not only in Basle, but also in Geneva, in Bern, in the Bernese territories, in France, Italy and the Württemberg Montbéliard. It was so violent that Calvin considered it necessary to justify his behaviour through the “Defensio orthodoxae fidei” (“Defense of the Right Faith”, 1554). In this document he keeps a record of the “heterodoxies” of Servet and tries to prove that the secular authority has to persecute heretics. Especially the Old Testament serves him as a proof; for instance, the verse Deuteronomy 13:6, in which God explicitly commands the killing of those who want to dissuade the people of Israel from the true faith.
Calvin's statements were in distinct contrast to a booklet that appeared in Basle at about the same time, entitled “Can Heretics Be Persecuted” (“De haereticis an sint persequendi”). It is initiated by the preface of Martin Bellius directed to Duke Christoph of Württemberg and completed by the contributions of a Georg Kleinberg and Basilius Montfort; names, behind which verifiable or most likely Sebastian Castellio is hidden.
The middle of the book is constituted by texts of the church fathers Augustin, Laktanz, Jerome and Chrysostom and other authorities of the history of church and reformation, who all oppose persecuting and killing heretics. Not only Luther, Erasmus, Johannes Brenz or Urbanus Rhegius are cited, but also Castellio and Calvin; the latter with an excerpt from his first “Institutio” of 1536, in which he calls for clemency and humanity towards excommunicated, Turks, Saracens and other enemies of religion.