The origin of Judaism is perhaps best illustrated in an ancient letter found in the great Cairo “geniza”. This letter describes a debate that took place nearly 1000 years ago in a land called Kuzar. The letter describes how Christian, Muslim, and Jewish wise men participated in an open panel debate (what is described is probably what later inspired R. Yehuda Halevi’s famous work – the Kuzari). The Muslims began by saying that G-d created the world in 7 days, chose the Patriarchs; Abraham, Issac and Jacob, and Jacob and his sons went to Egypt. There they multiplied and the L-rd took them out of Egypt. In the desert, he gave his chosen nation the Testament and 10 commandments. After this, the Jews sinned and thus a new revelation was granted to Jesus. Jesus’ followers also lost the true way and so He sent His prophet Mohamed who was given the holy Koran.
Both Jewish wise men and Christian wise men then began arguing with the Muslims and showing how this version could not possibly be true. Then the Christians spoke. They told precisely the same story except that they claimed that Jesus was the son of G-d and the ultimate redeemer. At this, both Muslim wise men and Jewish wise men argued the difficult philosophy. Then the Jews spoke. They described how G-d created the world in 7 days, chose the three Patriarchs and how Jacob and his 12 sons went to Egypt.
They described the revelation on Mount Sinai and the giving of the Testament and 10 commandments to the Jewish people. At this point, they stopped and you know what? No one argued at all! – So ends the letter written by the son of the King of Kuzar who describes how his father became a G-d fearing Jew. The letter is one of many findings on display of the great Geniza. I saw it when it was on tour but you can see it for yourself and verify the story (which is written in quite legible Hebrew!)
Jewish people have evolved Judaism
Of course, the history and development of the Jewish nation did not cease at Mount Sinai. In fact, it only just began. The years, trials and successes of the Jewish people have evolved Judaism into a very mature religion with extensive philosophical works and a great deal of literature. The Jewish religion has a built-in method for incorporating enhancing experiences into the Jewish religion such that it can continue evolving and developing. Current Jewish culture reflects the long history of this truly ancient and stalwart religion.
This construction of Judaism means that the various holidays and laws can generally be dated and perhaps best be understood as part of a series of layers.
The first layer is those laws and holidays that are laid down in the Pentateuch. These are the G-d given laws and their reasons are at least partially illustrated in the Bible itself (the Sabbath, Passover and the Day of Atonement are some examples).
Laws and Holidays of Jews
The next layer is the laws and holidays acquired or developed during the time of the first temple and the beginning of the second temple (Fine-tuning of various laws (dietary, Sabbatical and laws pertaining to cleanliness and uncleanliness) as well as the addition of Hanukkah and Purim). The text of Megillat Ta-anit is composed at this time and lists a wide variety of important historical dates.
Towards the end of the second temple with the impending exile and dispersion of the Jews throughout the diaspora, the development of written Jewish texts begin and thus a great deal of discourse develops around a variety of fine points in Jewish law (as is only natural when laws are attempted to be placed in writing). It is at this time that the daily prayer receives its formal thrice daily format and with the destruction of the second temple, becomes the primary form of worship.
Jewish culture undergoes even further refinement and evolution
The dispersal throughout the diaspora subsequently leads the Jews to lose touch with one another and slight variations in laws thus develop. Jews also are affected by the mentality and customs of the people around them and thus the Jewish culture undergoes even further refinement and evolution.
What we are witnessing today is a new phenomenon where these differing aspects of Judaism are becoming once more reunited and thus the best of all variation s are being forged into an even finer religion than ever.