The first five books of the Hebrew Bible (Genesis, Exodus, Leviticus, Numbers and Deuteronomy, a corpus named Torah) are read throughout the Jewish year every Shabbat. As a result, the text of these books was divided into fifty-four excerpts containing several chapters, called the Parashot. These fifty-four sections cover the whole year which is structured by a solar and lunar calendar. The simple year has twelve months. Seven times in a nineteen-year cycle, a thirteenth month is added, the second Adar, so that the feasts always fall in the same season. Since the lunar year has eleven days less than the solar year, it is necessary to add this month for the holidays to fall into the corresponding seasons. Thus the Passover will always fall in the spring. To read the whole of the Torah in one year with thirteen months takes fifty-four Parashot. With the “normal” year having only twelve months, two parashot are read together on some special Shabbats.
The division of the text into chapters came later, through the work of Christian scholars, and was also adopted by the Jewish tradition.
The first or one the first words of the verse that begins the parasha gives the title to the section. Thus, the first parasha begins in Hebrew by the word Bereshit (which is commonly translated into English as “In the Beginning”), the Hebrew title of the book of the Genesis.
The whole parasha is read every Shabbat in the synagogues, followed by an excerpt from the prophetic books on the same theme, called Haftarah. On Mondays and Thursdays, during the Morning Prayer, the first verses of the next parasha are read. This custom of public readings began in ancient times, because people would go to the markets and tribunals that met on these days.
It is sometimes the custom, among Orthodox Jews, to date letters or events with the name of the Parasha of the week, which also serves to designate the Shabbat. One speaks, for example, of "Shabbat Noah", or "Shabbat Ki Tissa", etc.
The cycle of readings ends and begins at the feast of Simchat Torah, which concludes the celebrations of the autumn feasts in the Jewish year.
According to tradition, the splitting of the text into parashot, which is itself the subject of commentaries, was established by the scribe Ezra upon the return from the exile of Babylon. According to the Talmud, it was Moses who instituted this organization of the text, and who set the three weekly readings, thus placing the reading of the Torah at the center of the liturgical life.
The Parashot are the subject of many commentaries, which sometimes refer to the exegetical methods of the Jewish tradition, such as the Midrash. The variety of the commentary reflects the richness of the text, and the creativity of those who tirelessly interpret it.