The original
concept dates back to the early days of
Christianity. The original
Christians were all
Jews, but there were some who wanted to, even felt they had to, spread the word to others. Others felt that it was wrong to include
Gentiles, non-Jews, as only the Jews were "God's chosen people." Legend, backed up by the
Epistles in the
New Testament, says that this debate dates back to Saints
Peter and
Paul.
Those who didn't want to preach to the Gentiles intended to retain all
Jewish customs and beliefs, amended only by the teachings of
Jesus. It was more of a
Revival of Judaism than a new religion. They maintained a society for a while, but ultimately they couldn't maintain their numbers, given that both Jews and Christians were being persecuted at the time. Over the ages, groups of Jews who
converted to Christianity have
rekindled the idea several times, but all - except for the current group - have died out.
Those who wished to spread their religion to others were forced to
assimilate others'
beliefs in order to draw converts. Eventually most Jewish customs were abandoned. This approach ultimately led to a much larger population base, as well as the ability to convert key officials (e.g.
Constantine). Thus these are the Christians we know today.