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Pope St. Gregory stigmatized Judaism and the Jewish People in many of his writings. He described Jews as enemies of Christ: "The more the Holy Spirit fills the world, the more perverse hatred dominates the souls of the Jews." He labeled all heresy as "Jewish", claiming that Judaism would "pollute [Catholics and] deceive them with sacrilegious seduction." The identification of Jews and heretics in particular occurred several times in Roman-Christian law,

According to Pope St. Gregory what religion must you be in order to be a heretic?
Jewish