Those Jews who in the past became apostates from Judaism to Christianity retained enough respect for Judaism to realise that they had changed from one religion to another. On the other hand, those Jews who died a martyr's death rather than become Christians did so because they thought that basic matters were at issue. To suggest that no important change has been made by moving from Judaism to Christianity is a peculiar insult to Judaism as an independent system of belief.
It is totally misleading to say that Jewish Christians are merely Jews who believe in Jesus as the Jewish Messiah. The Jewish concept of the Messiah is radically different from that of Christianity. The Christian concept of salvation through the death of a human divine Messiah is alien to Judaism, which refuses to regard any human being as divine, and regards a life acceptable to God as achievable by individual effort with the guidance of the Torah. In Judaism, the Messiah is an entirely human leader who is expected to preside over the messianic age of peace predicted by the prophets. He is much less central to Jewish than to Christian theology, since he is not regarded as providing the solution to the problem of human evil.
It is also wrong to make an analogy between modern Jewish Christians and early followers of Jesus in the Jerusalem Church. The best modern scholarship has shown that the members of the Jerusalem Church did not worship Jesus as divine or believe in the atonement of sins through the Crucifixion. They did not even practise the Eucharist, but instead relied on the Jewish sacraments of the Temple. They believed that Jesus was the human king of Israel who would soon return to claim his throne. In this attitude, they believed themselves, probably rightly, to be following the beliefs of Jesus himself. There is no modern form of Jewish Christianity that regards Jesus as a human claimant to the Jewish throne.
Leo Baeck College