is always the Sabbath preceding Pesach.
On these Shabbatot we do not have any special extra Torah reading in addition to Parashat HaShavua, but their special names denote another significant factor that distinguishes them from a ‘regular’ week. For example, on Parashat Beshalach the week’s Torah portion includes Shirat Hayam, lit., the songs or praises at the [Red] Sea sung by Moses, Miriam, and the men and women of Israel; thus its special name. Likewise, the other Shabbatot we mentioned have some significant factor to denote their special status and name.
However, the Four Parashiyot are different in that they have special Torah readings, as you noted. We will now discuss why we have these special Torah readings at this particular time of year.
The Gaon R. Shlomo Yosef Zevin, zt”l, discusses this very matter in his work HaMoadim BaHalacha (Jerusalem, 1956, p. 188), stating as follows:
“The unique importance of these parashiyot is found in Rabbinic literature. Even before the parashiyot of the Torah were divided among the Shabbatot of the year, the requirement [to read] the Four Parashiyot was already noted [Megilla 29a, Mishna]. However, in both the Mishna and the Tosefta we find no mention of the names of the weekly parashiyot [nor the requirement to read Parashat HaShavua].
“The requirement to read the Torah every Shabbat (in a congregation of ten) actually dates back to the time of Moses” (Bava Kamma 82a).
[The Gemara (ibid.) enumerates the 10 enactments of the prophet Ezra; among them was the public reading of the Torah on Shabbat at Mincha, as well as on the following Monday and Thursday, a cycle repeated every week. The Gemara then questions whether this was an enactment of Ezra and proves that the enactment to read the Torah on Shabbat as well as on Monday and on Thursday, dates back to Moses' time, derived from the verse ("Vayasa moshe et yisrael miyam suf vayetz'u el midbar shur) vayelchu sheloshet yamim bamidbar velo matz'u mayim -- (Moses brought the Children of Israel from the Red Sea and they went out toward the Desert of Shur) and they traveled three days in the desert and they did not find water" (Exodus 15:22).
The Gemara cites another verse (Isaiah 55:1), "Hoy kol tzamei le'chu lemayim. . . -- Everyone who is thirsty, go for water." Water is used to refer to the Torah. Thus one cannot go three days without thirsting for Torah and therefore we have a Torah reading every third day of the week.
The Gemara solves the apparent inconsistency by explaining that Ezra's enactment was to upgrade from reading a total of three verses to reading 10 verses, and calling up three people -- a Kohen, a Levi, and a Yisrael, each reading a minimum of three verses of the Torah.]
R. Zevin continues, “But the dividing of the Torah reading into 54 [weekly] parashiyot [each read on a Shabbat] came at a much later time. We find (Megilla 29b) that the Bnei Ma’arava in Eretz Yisrael, as opposed to the Diaspora [the Bnei Bavel], used to conclude a Torah reading cycle every three years.”
The Mechaber (Shulchan Aruch, Orach Chayyim 669:1) clearly states that on the second day of Shemini Atzeret, we in the Diaspora read in the first Torah scroll Vezot HaBeracha, the last parasha of the 54 in the Torah, until the conclusion. Then we read in the second scroll from Parashat Bereishit, the beginning of the Torah, until “Asher bara Elokim la’asot,” and in the third scroll we read the maftir, “Bayom hashemini atzeret,” as on the first day.
It is obvious that since the Gemara states that the Bnei Ma’arava would complete the Torah once every three years, we deduce that the Bnei Bavel (in the Diaspora) completed the Torah every year — even though the Gemara does not specifically say so. Thus, this Gemara serves as the source for the Mechaber and the Rema regarding that halacha.
To answer your second question first, we see that the division into parashiyot that we have today is inferred from this statement in the Gemara. The Four Parashiyot, however, and the time we read them, are clearly mentioned in the Mishna (Megilla 29a) by name. Therefore the Shabbatot on which one of them is read, as the Mishna delineates, are referred to by the parashiyot’s names.
(To be continued)