It has been argued that Judaism can be seen not only as a single religion, but as a group of similar religions. It has also been pointed-out that through all the trials and tribulations that Judaism has suffered through, that there have been common themes that have proven omni-pervasive. Any institution with roots as ancient and varied as the religion of the Jews is bound to have a few variations, especially when most of its history takes place in the political and theological hot spot of the Middle East.
In this discussion, many facets of Judaism will be examined, primarily in the three temporal subdivisions labeled the Tribal / Pre-Monarchy Period, the Divided Monarchy, and the Hasmonean / Maccabean and Roman Era. Among all the time periods where the religion has been split, these three seem to be the most representative of the forces responsible.
As for a common thread seen throughout all Judiasms, the area of topic will be covered in detail first, and then the multiple Judaism arguments will be presented. In this way, it is possible to keep a common focus in mind when reading about all the other situations in which the religion has found itself. A brief conclusion follows the discussion.
A Place to Call Home No other religion has ever been so attached to its birthplace as Judaism. Perhaps this is because Jews have been exiled and restricted from this place for most of their history. Jerusalem is not only home to Judaism, but to the Muslim and Christian religions as well. Historically this has made it quite a busy place for the various groups.
Jerusalem is where the temple of the Jews once stood; the only place on the whole Earth where one could leave the confines of day to day life and get closer to God. In 586 BCE when the temple was destroyed, no Jew would have denied Jerusalem as being the geographic center of the religion. From that point on, the Jewish people have migrated around the world, but not one of them forgets the fact that Jerusalem is where it all began. It is truly a sacred place, and helps to define what Judaism means to many people; a common thread to run through all the various splinters of the religion and help hold them together.
Even today, as the Jewish people have their precious Jerusalem back (through the help of other nations and their politics) there is great conflict and emotion surrounding it. Other nations and people in the area feel that they should be in control of the renowned city, and the Jews deny fervently any attempt to wrestle it from their occupation. It is true that there is no temple in Jeruslaem today, nor are all the Jews in the world rushing to get back there. But it is apparent that the city represents more to the religion of Judaism than a mere place to live and work. The city of Jerusalem is a spiritual epicenter, and throughout Judaism's long and varied history, this single fact has never changed.
Tribal / Pre-Monarchy
Judaism's roots lie far back in the beginnings of recorded history. The religion did not spring into existence exactly as it is known today, rather it was pushed and prodded by various environmental factors along the way. One of the first major influences on the religion was the Canaanite nation. Various theories exist as to how and when the people that would later be called Jews entered into this civilization. But regardless of how they ultimately got there, these pioneers of the new faith were subjected to many of the ideas and prejudices of the time. Any new society that finds itself in an existing social situation, can do no more than to try and integrate into that framework. And this is exactly what the Jews did.
Early Judaism worshipped multiple gods. One of these gods was known as Ba'al, and was generally thought-of as a 'statue god' with certain limitations on his power. The other primary deity was called YHWH (or Yahweh) and enjoyed a much more mysterious and illusive reputation. He was very numinous, and one was to have great respect, but great fear for him at the same time. Ba'al was not ever really feared, as his cycles (metaphorically seen as the seasons) were fairly well known, and not at all fear-inducing.
The fact that the early Jews and Canaanites had these two radically different representations of a deity active in their culture, basically assured that there would be splits in the faith. One group inevitably would focus on one of the gods, and another would focus on another. In this way, the single religion could support multiple types of worship, leading to multiple philosophies and patterns of behavior, which could then focus more and more on their respective niche, widening the gap into a clear cut distinction between religious groups.
This early time period was generally quite temporary and non-centralized, stemming from the fact that technology was at a very low level, and people's lifespan was fairly short. These conditions led to a rapid rate of turnover in religious thought, and left many factions of people to their own devices. Widespread geographic distribution coupled with poor communication certainly did not help in holding the many faiths together. The Tribal Period in Jewish history is one of the more splintered eras in the religion, but since these people were all living in the area near Jerusalem, the common thread can be seen clearly through the other less-defined elements of the religion.
By its very name, it is apparent that this period of history is host to a great deal of divergence in the Jewish religion. As Solomon was king, people began to grow more and more restless. Some objected to worshiping a human king, while others balked at the oppression of the poor that was going on. Political unrest in this period led to a decisive split in geographic territory, and thus a split in religious views.
A group of people left the area of Judah and traveled North to found Israel, where they could be free to practice their own political flavors, and their own religious flavors as well. This sort of behavior has come to be seen as common of oppressed people, and the result is almost always a great deviation in the ways of the 'old world'. A perfect example of this comes when examining the point in American history where independence was declared from England. Now, mere centuries later, America is as different in its politics, religions, and social forces from England as one could imagine. This was most likely the result when Israel was founded, far back in Biblical history.
Communication between the two cities was sparse. The priests and prophets were undoubtedly addressing items pertinent to one group, but not neccesarily the other. The influence of foreign traders to each of the two places, as well as the political attitudes of each all would have had enormous impact on a newly-spawned religion. Thus, it can easily be seen that the religion was split into (at least) two major divisions during this time period.
Toward the end of the Divided Monarchy, it seems that the prophets began calling for major changes in the basic foundation of the early Jews' lives. The kings and priests had no major disputes with the status quo, but apparently the prophets were calling for a reorganization. This sort of 'turmoil within' can do nothing but follow the kings and the priests, who have guided us and kept us safe? or follow the far-seeing prophets, who are more like us and honestly have our best interests at heart? As the next major historical division occurred this sort of argument would continue, and thus the Jewish people were left to practice their religion in whatever way many forms of Judaism as it existed toward the end of the Divided Monarchy.
Hasmonean / Maccabean and Roman Era
This time period in Jewish history is politically tumultuous, leading to high levels of splits and variations in the religion itself. One of the most disruptive types of all wars is a civil war. And this is exactly what occurs at the outset in the Jewish homeland of Jerusalem. The Jewish civil war was against the extreme Hellenizers (people who tended toward utter reason in their beliefs) and the moderate Hellenizers (people who can see things rationally, but believe there are more items to consider than this -- ex. the Maccabean family, who became the Hasmonean kings). So right away, it is apparent that the ideas that the Greeks introduced into Jewish culture have acted as time-bombs of social memes, and have created a major split in the religion.
When the violence of the war has subsided, the moderate Hellenizers have won ("everything in moderation!") and rule for a short time, until the Roman empire attacks and throws even more kinks into the Jewish society. When the Romans take over, the Hasmonean kings are left in place as 'puppet kings,' which ultimately forces the general population to question their governing body.
When the Romans destroy the temple in Jerusalem, it is made painfully clear that some changes are going to be made. Most obvious, the priests suddenly have no major role in the religion. Their primary purpose had been to tend to the sacrificing of animals, and since it is illegal to sacrifice an animal outside the temple, the priests were in an unsettling position.
As can be seen in countless other examples, politics and religion are invariably tied, and people began practicing their own flavors of Judaism after their civilization had been so radically altered. At this point in history, there is really no solid rule to prevent such splits, and for a time a mixed form of Judaism with many varieties flourishes.
No one was sure what to do once the heart of Judaism (the temple) had been destroyed, but it soon became apparent that an appealing option was arising. Two major social groups of the time period were vying for power. The first group, the Saducees were associated with the displaced Hasmonean kings. The second group, the Pharisees, had an idea that would help work around the tragic destruction of the temple. People were split, once again. They could stay with the traditional Saducees (who had the political power, believed in only written Torah, and did not subscribe to resurrection -- basically a conservative view), or they could side with the newcomers, the Pharisees (who had religious power, believed in both the written and the oral Torah, and believed in resurrection) and hope to preserve their Jewish heritage by worshiping outside of the temple, in their everyday life.
It was not a hard decision, and the Pharisees eventually gained power, leading the Jewish religion into its next phase of Rabbinic Judaism. It is apparent that in each of the three time periods discussed above that many factions of the same religion were active. Competing philosophies, outside political forces, and geographic isolation are among the most obvious of the dividing forces. However many other influences 'pound' each and every day on a given social institution, subtly forming it and changing it into something it was not. For this reason, the answer to the debate whether Judaism is a single, or multiple religion(s) is an obvious one, depending upon how you choose to look at it. Every religion has many pieces, but as long as there are a few constants (such as the birthplace, the language, literature, etc) it is possible to view the whole as a single force, and still acknowledge variations that will inevitably spring-up.