We have finished the halachos of ervah, and will discuss the four parshiyos.
The four parshiyos, Shekalim, Zachor, Parah and Hachodesh, are read in conjunction with the month of Adar. There are occasions where parshas Shekalim falls out on Rosh Chodesh, but it is never later than Rosh Chodesh Adar. Parshas Hachodesh is always before or on Rosh Chodesh Nissan, and never after. Parshas Zachor and Parshas Parah are in the middle of the month of Adar.
Chazal explain why they enacted reading these parshiyos:
- Shekalim: the Torah tells us that starting in Nissan, korbanos brought in the Beis Hamikdash need to be brought from the new half shekels collected from every household in Klal Yisroel. Thus, they would collect the half shekalim in the month of Adar so they could be used in the Beis Hamikdash in Nissan. This parsha was already read at the time of the Beis Hamidkash, in order to announce the collection of the shekalim. We continue this laining along the lines of a tefillah, that we should be zoche to the return of the korbanos.
- Zachor: this parsha is always read on the Shabbos immediately prior to purim. Although zechira, remembering, is often thought of as something done in the mind, it can also mean something which should be memorialized, i.e. expressed. The Gemara learns that this remembering must be read from a Sefer Torah. Chazal instituted that we should read it once a year, as people tend to remember things for about one year. Chazal enacted that it should be read immediately preceding Purim, since Klal Yisroel were successful in eliminating some of Amalek through the Purim story.
- Parah: the Shulchan Aruch writes that some opinions (yeish omrim) hold this parsha is a chiyuv deoraysa. He does not bring other opinions. When the Shulchan Aruch uses such language, it is an indication that even though it is only written in some sources, the other rishonim do not disagree, so it is assumed to be accepted. The Mishnah Berurah brings achronim who disagree.
At the time of the Beis Hamikdash, it served to remind Klal Yisroel to purify themselves properly in order to be ready for the korban pesach. Nowadays, it serves as a tefillah that we should be zoche to have the Beis Hamikdash once again, and be able to use the taharah which the Beis Hamikdash offered.
- Hachodesh: to announce the beginning of the new year in terms of the months of the new year. We lain it as a reminder that Hashem enacted the months and years to remind us about Klal Yisroel leaving Mitzrayim.