Commentary for Megillah 3:4
רֹאשׁ חֹדֶשׁ אֲדָר שֶׁחָל לִהְיוֹת בְּשַׁבָּת, קוֹרִין בְּפָרָשַׁת שְׁקָלִים (שמות ל). חָל לִהְיוֹת בְּתוֹךְ הַשַּׁבָּת, מַקְדִּימִין לְשֶׁעָבַר וּמַפְסִיקִין לְשַׁבָּת אַחֶרֶת. בַּשְּׁנִיָּה, זָכוֹר (דברים כה). בַּשְּׁלִישִׁית, פָּרָה אֲדֻמָּה (במדבר יט). בָּרְבִיעִית, הַחֹדֶשׁ הַזֶּה לָכֶם (שמות יב). בָּחֲמִישִׁית, חוֹזְרִין לִכְסִדְרָן. לַכֹּל מַפְסִיקִין, בְּרָאשֵׁי חֳדָשִׁים, בַּחֲנֻכָּה וּבְפוּרִים, בַּתַּעֲנִיּוֹת וּבַמַּעֲמָדוֹת וּבְיוֹם הַכִּפּוּרִים:
If Rosh Chodesh Adar falls on Shabbath, we read (maftir) in the section of shekalim [(Exodus 30:11-16) to apprise them to bring their shekalim in Adar so that offerings may be brought from the new donations on the first of Nissan.] If it falls out during the week, it is read on the preceding (Shabbath), [even if Rosh Chodesh Adar falls out on Sabbath eve.] And we break off until the next Shabbath. [i.e., we do not read the second section ("Zachor") so that it be read on the Shabbath preceding Purim, to link the erasing of Amalek with the erasing of Haman.] On the second (Sabbath), "Zachor" (Deuteronomy 25:17-19). On the third, parah adumah (the red heifer) (Numbers 19) [to exhort Israel to cleanse themselves in order to bring their Pesach offerings in cleanliness. Which is the third Sabbath? The Sabbath after Purim. And when Rosh Chodesh Nissan falls out on Shabbath, the third Shabbath is the one before Rosh Chodesh Nissan. (It is read) in order to link the exhortation to cleansing oneself from dead-body uncleanliness to the Pesach offerings.] On the fourth, (Exodus 12:1-20): "This month is unto you" [containing the section on Pesach]. On the fifth, the usual order (of haftaroth) is reverted to. [For until then, the haftarah is of the nature of the four sections, viz. "shekalim" — (I Kings 12:1); "Zachor" — (I Samuel 15:2); "Parah" — (Ezekiel 36:25); "This month" — (Ezekiel 45:18). And from that time on, the haftarah, again, is of the nature of the section of the day.] For all (of the following) we break off [i.e., We do not read a haftarah which is of the nature of the section, but one which is of the nature of the day]: Rosh Chodesh, Channukah, Purim, fasts and ma'amadoth, and Yom Kippur.
Bartenura on Mishnah Megillah
English Explanation of Mishnah Megillah
On the second [of the special Shabbatot] they read “Zakhor;”
On the third the portion of the red heifer;
On the fourth “This month shall be for you;”
On the fifth the regular order is resumed.
They interrupt [the regular order] for anything: for Rosh Hodesh, for Hanukkah, for Purim, for fasts, for Ma’amadot, and for Yom HaKippurim.
The rest of this chapter deals with the portions of the Torah read on holidays and special Shabbatot. In mishnaic times they did not complete the Torah once a year as they did in Babylonia and as we do today, but rather about once every three years. Another difference between the ancient custom and that of today is that today when certain holidays fall on Shabbat we read the regular Torah portion and then we add a special reading for that day. In mishnaic times, since they didn’t really have a regular Torah portion, they only read the special reading. Thus if Rosh Hodesh fell on Shabbat they would read only the portion for Rosh Hodesh and interrupt the regular continuous reading of the Torah.
Our mishnah deals with the four special Shabbatot that precede Pesah. They are:
1) Shekalim to remind people that on Adar they would have to bring the half-shekel to the Temple (see tractate Shekalim). This was read before Rosh Hodesh Adar.
2) Zakhor Deuteronomy 25:17-19. This is read before Purim and connects Amalek with Haman.
3) Parah Numbers 19. We read about the red heifer to remind people that before Pesah they must be pure in order to eat the Pesah sacrifice.
4) Hahodesh Exodus 12:1-20. Read the Shabbat before Nissan to remind people that Pesah is approaching and that they must begin preparing.
Section one: On Rosh Hodesh Adar which falls on Shabbat they read Shekalim, which is Exodus 30:11-16. However, if Rosh Hodesh Adar falls during the week, they would read Shekalim on the Shabbat before Rosh Hodesh. On the Shabbat following Rosh Hodesh they would go back to reading where they had last left off in the regular cycle. This week would then be a break from the four special portions enumerated in our mishnah.
Sections 2-5: The mishnah now enumerates the four special portions, described above in the introduction. After Hahodesh, the order returns to its regular cycle. We should note the concept of Shabbat Hagadol, the Shabbat before Pesah, did not exist in mishnaic or talmudic times.
Section six: The regular reading of the Torah is interrupted for any special occasion. This includes all holidays. On fast days, meaning Mondays or Thursdays when they would fast for rain, they would not read the regular portion but rather the special readings for fasts. Ma’amadot were described in greater length in tractate Taanit. These were gatherings by people in towns when their kohanim would go to the Temple. The people in the town would read from the beginning of Genesis and not from the regular Torah portion.