Each spring, we read four special portions from the Torah, along with the weekly portions. The first of these is Parashat Shekalim (Exodus 30:11-16), which deals with the law of the half-shekel. This offering brought to the Tabernacle became a tax used to support the Temple. It was collected each spring, so Shabbat Shekalim is the Shabbat preceding or coinciding with Rosh Hodesh Adar.
The second of the four portions is Parashat Zakhor (Deuteronomy 25:17-19), which includes the commandment to remember and wipe our Amalek, the prototypical enemy of the Jews. This portion is read on the Shabbat preceding Purim, because Haman was supposed to be a descendant of Amalek.
The third portion is Parashat Parah (Numbers 19:1-22), which details the law of the red cow, used in the ritual of purification after contact with a corpse. This portion is read when it is, presumably because, in the days of the Temple, people had to undergo this purification ritual before they could partake of the Paschal lamb in Jerusalem.
The fourth portion is Parashat Hahodesh (Exodus 12:1-20), which sets down some of the observances of Pesah. Shabbat Hahodesh precedes or coincides with Rosh Hodesh Nisan, the month in which Pesah occurs. Each of the four portions has a special Haftarah to go with it.
