Just as medieval Christian theologians thought through the categories of women and heretics, they also focused upon Jews as a point of difference. The idea of Jewish difference was a crucial category of selfunderstanding within Christian theology. The history of Christianity as a religion was founded on the moment of separation from Judaism. From the outset, Christianity had negotiated its identity in relation to the Judaism from which it emerged. On the one hand, Christianity superseded Judaism—the revelation of Christ as Messiah completed the prophecies of the Hebrew Bible. Christ repaired the damage that Adam and Eve had done, and rendered null and void the Law that Jews had practised in order to show their respect for God. On the other hand, Christianity only made historical sense if the truth of the Hebrew Bible was respected. Christ's salvific work was only legible if Jewish history was taken into account. Therefore, Christianity was of Judaism and yet repudiated it entirely. Christianity needed Judaism to understand its own foundations, and its own saving work. At the same time, Jews failed to recognize Christ as Messiah, and in so doing had sinned most grievously. The category of the Jew, therefore, presented a challenge to the theologian. It was necessary to find a way to recognize Christianity's Jewish foundations in order to explain just how Christ was able to fulfil the messianic expectation of the Hebrew Bible. Yet, the Jews bore responsibility for Christ's death, in as much as they gave him over to Roman authorities. As such, they were both origin and other to the Christian tradition.

Adam and Eve's sin was necessary for Christian history to begin, as we have seen. This necessity, however, provided no mitigation for their sin. Similarly, Christ needed to be put to death in order to be able to rise from the dead. Christian history is dependent on the crucifixion as the catalyst for the momentous event of the resurrection. The Jews, however, were still to be judged for their failure of recognition, even though their socalled obduracy was in fact enabling for Christian history. In response to this ambivalent status, Augustine of Hippo formulated a doctrine of Jewish witness that obtained well into the Middle Ages. He argued that it was God's will that Jews be tolerated until the end of time, as they provided a living witness to the foundations of Christianity.