I have been asked on Comment Is Free to explain my contention that Christianity was not born out of Judaism. I'm also posting my explantion here: all comments gratefully received, of course.
Christianity is the recapitulation in Christ of the Old Israel, of Hellenism, and of the Roman Empire, first in the Person of a Jew in what is now recognised to have been a profoundly Hellenised Roman province, and thereafter (i.e., after His Ascension) in His Mystical Body, the Church. The Incarnation culminates, completes and surpasses the providential raising up and interaction of the Old Israel, of Hellenism, and of the Roman Empire.
Judaism is also a product of that interaction (the term "Early Judaism" refers to Judaism, at, only just before, and only just after the time of Jesus, not, say, to David, or even Moses, or even Abraham), but reacted in a strongly Semitic way against the rise of Christianity. Islam is also such a Semitic reaction, just as there were and are Hellenistic, Roman, and Graeco-Roman reactions (A C Grayling, for example, exhibits a strong tendency in this regard).
Judaism even defined its Biblical Canon (which it had not previously done) in such a way as to exclude books likely to lead people into Christianity, and therefore already included in the Christian Canon; a key fault is Protestantism is the naive and incorrect acceptance of the 39-book Jewish Canon as "the Bible of Jesus and the Apostles", when in fact it is an explicitly anti-Christian invention. Furthermore, Judaism hardly deals with the Biblical text directly, preferring layer upon layer upon layer of Rabbinical commentary upon Rabbinical commentary upon Rabbinical commentary.
Anthropologically, sociologically, and so forth, Christianity and Judaism are as much or as little the continuation of the religion of the Hebrews. To hold one or the other to be so is to assent to a theological proposition, to make a leap of faith. But they cannot both be so, and recent attempts to claim that they are have only ended up, whether or not the well-meaning protagonists admit it, in effectively concluding that neither of them is.