"If someone appears to us to be such a foreign body within his time and environment as not really to belong to it, then a historian would more likely suppose that we do not know enough about his time and environment. Correspondingly, it is valid to say with regard to Jesus that, if on the basis of some words and deeds Jesus sppares in the eyes of many theologians to have left the world of Judaism, it more liekly means that theological scholarship does not yet know this world well enough to judge what was or was not possible and conceivable within it."
In fact, simply chalking up other material deemed non-authentic to the influence of the early Church won't solve the problem since Matthew, Peter, Paul, etc., were all Jews!
So what of the role of Baptism and the celebration of the Eucharist in the New Testament? Many deny such things can be traced back to Jesus himself, recognizing them as later Christian "additions" to the Jesus tradition?
But, again, such an approach fails to account for the Jewishness of the early Church.
Could it be that perhaps we haven't yet adequately understood the cultic understanding of first-century Jews? Perhaps such an understanding could shed light on the development of the Christian cultic practices. Could it be that Christian rites flow from Jesus, a Jew?
Well, that in a nutshell is what I'm working on answering in my dissertation...