[The sack of Jerusalem depicted on the Arch of Titus]
Bishop John Shelby Spong greatly illuminated this subject for me in his book, Liberating the Gospels. Spong explains that it was the fall of Jerusalem and the fight over the Jewish Scriptures (the OT) that caused the early Christian church to begin moving away from their Jewish roots.
"It was the fall of Jerusalem, with its resulting destruction of the Temple and the priesthood, that raised the price of that uneasy accommodation to such painful levels that fracture was inevitable. The intolerable quality of this event did not appear all at once. Rather its intensity grew from the moment of Jerusalem's defeat over the next twenty years, until the separation was so total and so hostile that finally the Jewish Christians were literally expelled from the synagogues. As this tension built towards its climax, both Christian hostility toward heterodox Jewish Christians expanded. Echoes of this rising hostility can be found quite overtly in the Gospels. As the rhetoric heightened, the lines around what Jews could tolerate inside Judaism tightened considerably and those heterodox Jewish Christians, offended by this increasing hostility, began to move more and more into gentile circles." (Liberating the Gospels, "How These Jewish Books Became Gentile Captives")With the heart of Jewish life demolished the one thing that kept, and continues to keep, the Jews together was their scripture. Judaism depended on their scripture as the final existing thread to their identity and their survival. Without it Judaism may have disappeared into history only to be mentioned in Christian history books. The post- 2nd Temple Jews also developed a new form Judaism, Rabbinic Judaism. In this new form of Judaism both the written and Oral Law took center stage, which caused a widening rift between Jews and the Early church, which at the time was growing into a Gentile majority, to become a full blown break over the battle over scriptural interpretation. The Jews protected the one link that bounded them together, while the gentile Christians found new interpretation in the Jewish scripture that they saw pointed to the Risen Christ. The Jewish Christians, caught in the middle, lost out in the end as the movement became overwhelmingly gentile the Jewish born Christians would eventually die out. Yet without the connection to Judaism through the Jewish Christians, Christianity may not have had a strong enough root to compete with the ancient Greco-Roman religions. It's tough being the new kid on the block, just ask the Mormons.
I agree with Spong that the destruction of the Temple and the subsequent battle over the Jewish scripture were the main causes of the Jewish Christian rift in the Early Church. Spong brought up an intriguing although highly controversial view of the development of the gospels: the gospels were written as "collections of expository teaching or preaching that had been created in the same way that the rabbis would create what came to be called the midrash rabbah." ("How These Jewish books became Gentile Captives", pg. 52) The gospels were written to help explain (and later remember) what they experienced through the Risen Christ by searching through the Jewish scripture for new meaning. To traditional Christians this translates as the early church invented Jesus as a vehicle for new teachings, yet this creative writing is riddled throughout Jewish literature. So the question then becomes how do we read the "eyewitness" accounts found in the gospels? How much of the gospels were elaborations made by the Christian church and how much are historical? All, some, none?
In this case, pronouncement stories, stories which surround a particular teaching or saying of Jesus, could have been written by the Jewish Christians as a creative foundation for a teaching of Jesus. The focus of the pronouncement stories is the pronouncement itself and not in the detail of the story, which gives the story flexibility when retold. A storyteller knows the basic structure of a story while she/he weaves his or her own creative aspects into the tale. This is how oral stories were told and retold until they were preserved in writing. It was when the story moved from the oral tradition to written, from Jewish to Greek that the words in the gospels moved from a new creative interpretation on experiencing God towards Christian Orthodoxy.