Briefly, here is how it all happened. The meaning of the term "Christian" dates from after Jesus, and was really of dubious value, because thousands of creeds considered themselves Christian. That all changed in 325 at the Council of Nicea, when the emperor Constantine to all intents and purposes poured the whole thing in a meatgrinder, and made hamburger out of it, which was then promoted as Christianity, he created the brand, and in effect put the Church in business but good. Or, to describe it a little bit more literally, he brought this council together and more or less forced the various factions to come up with one common denominator of what made a Christian a Christian - what became the Nicene Creed - and thus he forced a certain homogeneity, which had never existed beforehand, and which in all reality never existed since either, but for a while it seemed that way. After that the first major rift was the Eastern and Western churches, or Greek Orthodox, vs. Roman Catholic, which became final in the 11th century. This carries on without many further overt problems until the time of the reformation, when Luther took issue with some of the theological wild growth in the Church, and his response to what he saw was to try to go back to the literary source, i.e. the Bible. He then translated it into the vernacular, and advocated everyone's right to have their own relationship with this material, though he evidently certainly intended to be helpful with the proper interpretation. By the present time we are back where we started, for there are at least as many versions of Christianity now as there were in the centuries immediately after Jesus.
With the enlightenment, along with the progress of archaeology, Biblical scholarship became interested in the connection between textual scholarship and archaeology, realizing that it might be possible to gain a much deeper knowledge of the history behind the Bible this way. This unleashed a whole new energy that was focused on the historical basis of the tradition. Naively, many of these scholars thought that with this sort of scientific basis to their faith, they could save Jesus from Catholicism. Of course what happened over time was that Catholics also became interested and after Vatican II essentially co-opted the search for the historical Jesus. If you really get excited about all the variations on the theme, there is an excellent summary of the whole story on a website on Early Christian Writings, here: http://www.earlychristianwritings.com/schweitzer/index-2.html.
The whole endeavor has fueled controversy, instead of leading to answers. It is a further evolution within the Christian tradition, and has led only to a proliferation of theories about Jesus, which sort of compete with interpretation of Paul. The interpretation of Paul c.s. sort of won out in the past, and became Christianity. Today we have a seemingly ever expanding universe of interpretations of him based on all sorts of criteria. The variations are interesting at times, declaring him to be a myth created by Paul, or explaining him as a revolutionary, where some have Paul as a Roman spy, seeking to subvert the movement. Yet none of them have much relevance from the standpoint of anyone who decides to try and practice what Jesus teaches. The only path to him, is to follow him, not to study his worldly circumstances, and write and rewrite the history of his appearance in the world two thousand years ago. For anyone who has studied the lives of saints, it should be obvious that experience was the dominant factor, which is exactly why the Church so often had trouble with accepting saints for what they were, and became entangled in their theological acceptability.
With a slight play of words, we could say, do not let the historical Jesus delay you, or, in the words of the Course:
The ego will demand many answers that this course does not give. It does not recognize as questions the mere form of a question to which an answer is impossible. The ego may ask, "How did the impossible occur?", "To what did the impossible happen?", and may ask this in many forms. Yet there is no answer; only an experience. Seek only this, and do not let theology delay you. (ACIM:C-in.4)