The history of Jewish-Christian relations is complex and difficult. Alongside the positive moments, in which several bishops took the Jews under their wing to protect them from progroms or mass extermination, there were dark periods that have remained particularly deeply impressed in the Jewish collective conscience. On the Catholic side, Nostra Aetate, the Second Vatican Council's Declaration on the Relations of the Church to Non-Christian Religions was the decisive turning-point. It was irrevocable, as Benedict XVI also reaffirmed clearly during his visit to the Synagogue of Rome on 17 January 2010. It was irreversible for the simple reason that the main theological arguments of Nostra Aetate were firmly established in two of the Council's most important Constitutions: the Dogmatic Constitution on the Church (nn. 6, 9 and 16) and the Dogmatic Constitution on Divine Revelation (nn. 3, 14).
To describe the relationship between Judaism and Christianity the image Paul used in his Letter to the Romans may perhaps be more useful than a conceptual explanation. He spoke of the root of Israel on to which the wild branches of the Gentiles were grafted (Rom 11:16-20). This image, reminiscent of the Prophet Isaiah (11:1), expresses in two ways the meaning of distinction in unity. On the one hand St Paul says that the grafted wild branches did not grow from the root itself and could not derive from it. On the other hand the Church must draw her strength and vigour from the root that is Israel. If the grafted branches are cut from the root, they wither, weaken and, finally, die.