The twelfth and thirteenth centuries were also characterized by the broadening of the horizons of Europe that took place in the wake of the Crusades; indeed, the rise of heresy in Western Europe may have been stimulated by the new contacts between East and West. These contacts with the Muslim world aided Jewsish apologists in a very old and critical area of polemic, namely, the Christian argument that the success and wide diffusion of Christianity proved its superiority over a religion with a small number of adherents who were growing progressively weaker. Jews could now argue with genuine conviction and greater effectiveness that even by the numerical test alone, Christianity would not prevail; Muslims, they said, rule "half the world," and God's promise to Abraham that all nations of the world would be blessed in him and his seed was certainly not fulfilled through Christianity. Jews even attempted to make Christians feel isolated by arguing that the disgust at eating pork was really a consensus omnium with the sole of exception of Christians. In fact, even the existence of Christian heresy could be cited as proof of the limited extent of orthodox Christianity. Finally, the failure of the Crusades was cited to show that the alleged success of Christianity was illusory; consequently, Christians would have to admit that temporal success is unrelated to religious truth. Once this admission was made, the old argument against Judaism would have to be abandoned.
David Berger (Page 29 of his Introduction to the Niẓẓaḥon Vetus)
