Nachmanides, first as rabbi of Girona and later as chief rabbi of Catalonia, seems to have led a largely untroubled life. When well advanced in years, however, his life was interrupted by an event which made him leave his family and his country and wander in foreign lands. This was the religious disputation in which he was called upon to defend his faith in 1263. The debate was initiated by a Pablo Christiani, a Jewish convert to Christianity, who had been sent by the Dominican Master General, Raymond de Penyafort, to King James I of Aragon, with the request that the king order Ramban to respond to charges against Judaism.
Pablo Christiani had been trying to make the Jews convert to Christianity. Relying upon the reserve his adversary would be forced to exercise due to fear of offending the feelings of the Christians, Pablo assured the King that he would prove the truth of Christianity from the Talmud and other rabbinical writings. Ramban answered the order of the King, but asked that complete freedom of speech should be granted. For four days (July 20–24) he debated with Pablo Christiani in the presence of the King, the court, and many churchmen.
The subjects discussed were:
Christiani argued, based upon several aggadic passages, that the Pharisee sages believed that the Messiah had lived during the Talmudic period, and that they ostensibly believed that the Messiah was therefore Jesus. Nachmanides countered that Christiani's interpretations were distortions; the rabbis would not hint that Jesus was Messiah while, at the same time, explicitly opposing him as such. He further said that if the sages of the Talmud believed that Jesus was the messiah then most certainly they would have been Christians and not Jews, and the fact that the sages of the Talmud were Jews is beyond dispute. Nachmanides proceeded to provide context for the proof-texts cited by Christiani, showing that they were most clearly understood differently than as proposed by Christiani. Furthermore, Nachmanides demonstrated from numerous biblical and talmudic sources that traditional Jewish belief ran contrary to Christiani's postulates.
Nachmanides argued that the Biblical prophets regarded the future messiah as a human, a person of flesh and blood, and not as divine, in the way that Christians view Jesus. He stated that their promises of a reign of universal peace and justice had not yet been fulfilled, that since the appearance of Jesus, the world had been filled with violence and injustice, and that among all denominations the Christians were the most warlike."[... it seems most strange that... ] the Creator of Heaven and Earth resorted to the womb of a certain Jewish lady, grew there for nine months and was born as an infant, and afterwards grew up and was betrayed into the hands of his enemies who sentenced him to death and executed him, and that afterwards... he came to life and returned to his original place. The mind of a Jew, or any other person, simply cannot tolerate these assertions. You have listened all your life to the priests who have filled your brain and the marrow of your bones with this doctrine, and it has settled into you because of that accustomed habit. [I would argue that if you were hearing these ideas for the first time, now, as a grown adult], you would never accept them."
He noted that questions of the Messiah were of less dogmatic importance to Jews than most Christians imagine. The reason given by him for this bold statement was that it was more meritorious for the Jews to observe the precepts under a Christian ruler, while in exile and suffering humiliation and abuse, than under the rule of the Messiah, when every one would perforce act in accordance with the Law.
As the disputation seemed to turn in favor of Nachmanides, the Jews of Barcelona, fearing the resentment of the Dominicans, entreated him to discontinue; but the King, whom Nachmanides had acquainted with the apprehensions of the Jews, desired him to proceed. The controversy was therefore resumed, and concluded in what was considered a complete victory for Nachmanides, who was dismissed by the King with a gift of three hundred gold pieces as a mark of his respect. The King remarked that he had never encountered a man who, while yet being wrong, argued so well for his position.
The Dominicans, nevertheless, claimed the victory, and Nachmanides felt obligated to publish the text of the debates. From this publication Pablo selected certain passages which he construed as blasphemies against Christianity and denounced to the head of his order, Raymond de Penyafort. A capital charge was then instituted, and a formal complaint against the work and its author was lodged with the King. James was obliged to entertain the charge, but, mistrusting the Dominican court, called an extraordinary commission, and ordered that the proceedings be conducted in his presence. Nachmanides admitted that he had stated many things against Christianity, but he had written nothing which he had not used in his disputation in the presence of the King, who had granted him freedom of speech.
The justness of his defense was recognized by the King and the commission, but to satisfy the Dominicans, Nachmanides was sentenced to exile for two years and his pamphlet was condemned to be burned. He may also have been fined, but this was lifted as a favor to Benveniste ça Porta, who according to some authorities (Graetz Gesschichte der juden Vol. VII pp. 440–441;, Chazan, Barcelona and Beyond, p. 199), was Nachmanides' brother. The Dominicans, however, found this punishment too mild and, through Pope Clement IV, they seem to have succeeded in turning the two years' exile into perpetual banishment.
Other scholars believe that the identification of Bonastruc ça Porta with Nachmanides is incorrect (Mayer Kayserling JQR Review 8, 1896, p. 494). If their view is correct than there were actually two people who were found to be blasphemous in the same time period and location.