There were two other types of heresy against which [Bernard Gui] warned his fellow inquisitors. One of these he called “the perfidy of the Jews”. Now, in fairness to the Holy Office, it must be noticed that never, in its entire history, did it proceed against the Jews, either on racial grounds as Jews, or on religious grounds as members of the synagogue. Far from attacking the Law of Moses, it defended that revelation against certain sects of heretics, as an essential part of Catholic truth. Over the Jew as Jew it claimed no jurisdiction. It was a Christian tribunal, which concerned itself with Jews only when they were Christians, or when they went out of their way to commit offenses against Christians, either by deriding Christian beliefs or ceremonies, or by persuading Christian to give up the Faith.
That the Jews, scattered throughout Christendom, carried on a continuous and effective propaganda which, while it persisted, was bound to make impossible the complete Christianizing of society, is freely admitted by Jewish scholars, as I have taken note elsewhere.
William Thomas Walsh, Characters of the Inquisition (1940)