Those familiar with synagogue ritual know that there is a weekly Torah reading cycle. In the Fall, there are the inspiring stories of creation and the history of the origins of the Jewish people (Genesis). With winter comes the enslavement, freedom, and the journey in the wilderness (Exodus). Winter thawing into spring brings the laws of the Temple (Leviticus), followed by additional Temple laws and more of the wilderness history (Numbers). Finally, as summer fades into fall, there is a summation of the entire history of Israel as seen through the eyes of our great leader Moses (Deuteronomy).
But this was not always the Torah reading cycle shared by all Jews. In some Jewish communities, the reading of the Torah was spread out over a three year period, rather than one year.
Both reading cycles have historical roots. While the reading of the Torah on a weekly basis was mandated by the Torah, the exact amount to be read was not originally specified, and two different traditions emerged.
In the cities of ancient Israel, the custom was to divide the Torah into 155 parts, which spread the reading over a three year period. This tradition is still followed in some Reform and Conservative synagogues today.
In the cities dominated by the Jewish leaders of Babylon (post-Roman exile), it became the custom to divide the Torah into 54 portions (parashiot). Depending on whether the year was a leap year or not, certain parashiot were combined. The divisions in this annual cycle ensured the fulfilment of the instructions of Ezra the Scribe: that the section of “curses” in Leviticus (parashat B’chukotai) be read just before Shavuot and that the great rebuke in Deuteronomy (parashat Kee Tavo) be read just before Rosh Hashana.