The two final Parshiyot of the Book of Bamidbar, Matot and Masei, are, in the vast majority of years, combined into a single reading. In some years, however, we read the two separately, on two different Shabbatot. On such years, of course, we read the first section of Parashat Masei at Shabbat Mincha and on Monday and Thursday morning in the week prior to Shabbat Parashat Masei. This section lists the forty-two "Masa'ot," the stations where Benei Yisrael encamped during their forty-year sojourn in the wilderness.
We find divergent customs with regard to this reading. All our Siddurim present as the reading during the week before Shabbat Parashat Masei only the first eleven verses of this Parasha. However, the Magen Avraham (commentary to the Shulchan Aruch by Rabbi Avraham Gombiner, Poland, 1637-1683) cites (in Siman 428) a ruling from the work "Tzeror Ha'mor" that the list of the forty-two "Masa'ot" must always be read in its entirety; a congregation should not read on any given occasion only some of the "Masa'ot." The reason given is that the forty-two "Masa'ot" correspond to the forty-two-letter Name of God. All forty-two must therefore be read together, as a single unit, and not divided into separate sections. This is the ruling as well of Rabbi Chayim Palachi (Turkey, 1788-1868), in his work Kaf Ha'chayim (Siman 428).
I consulted Chacham Yom-Tov Yedid, the authority on the customs of Halab, and he reported that the Halab community indeed followed this ruling of the Magen Avraham and Kaf Ha'chayim, though the custom changed when the community arrived in the United States. Practically speaking, each community should follow their accepted custom, though we should nevertheless be aware of the practice that was observed in earlier generations.
