וַיָּבֹאוּ הָאֲנָשִׁים עַל הַנָּשִׁים כֹּל נְדִיב לֵב הֵבִיאוּ חָח וָנֶזֶם וְטַבַּעַת וְכוּמָז כָּל כְּלִי זָהָב וְכָל אִישׁ אֲשֶׁר הֵנִיף תְּנוּפַת זָהָב
The men came with the women; every generous hearted person brought bracelets and earrings and rings and buckles, all kinds of golden objects, and every man who (donated a donation) of gold...
The Daas Zekeinim there explains that the women refused to donate their jewelry for the creation of the Eigel. What they did give, they gave under duress. Now, when the call went out for donations for the Mikdash, the men wondered if the women would be willing to give anything. As it turned out, the women dragged their husbands with them and thronged Moshe Rabbeinu, insisting that he take their golden jewelry (as the Ramban, Ibn Ezra, and Rabbeinu Bachay also say). Whereas they had to be coerced to give for the Eigel, for the Mishkan they were more enthusiastic than the men.
The Daas Z'keinim continues and says that if they had been unwilling to give their jewelry in both cases, it wouldn't prove anything. Maybe they simply loved their jewelry and wouldn't give it away for any reason. But their enthusiasm about giving to the mikdash conclusively proved that they were motivated by a spiritual refinement which led to an abhorrence of the Golden Calf and an enthusiastic nedivus for the Mishkan. In commemoration of this spiritual greatness, they were given as an eternal holiday the day the Mishkan was erected, Rosh Chodesh Nissan. Along with that Rosh Chodesh, they were given every Rosh Chodesh of the year as well. The primary celebration, however, the Mother of the Yom Tov, is Rosh Chodesh Nissan. (Much of this is not in the printed Daas Z'keinim. It's an interpretive reading based on my expertise in his style of writing.)
There are many references to this odd yomtov. The most famous is the Yerushalmi in Pesachim 4:1 and Taanis 6:1 that says that for such women who have a minhag to not work on Rosh Chodesh, it is a valid minhag. This Yerushalmi is cited by the Rashba in Teshuvos 306 and the Rosh in Megilla 3:4 and the Mordechai in Shabbos 2:278. Rashi also mentions it there in Megilla on 22b, and Tosfos brings the idea from the Pirkei D'Rebbi Eliezer Perek 45.
The Yerushalmi does not explain the source of the minhag, but the Pirkei D'Rebbi Eliezer does, referring to the events of the Eigel. The part about their rushing more excitedly than the men to give away their jewelry to build the Mishkan does not appear in most editions of the Pirkei D'Rebbi Eliezer.
Since women are mentioned several times as having spun wool and linen for the Mishkan, in many places the minhag eventually became limited to not spinning thread Rosh Chodesh. Since nobody spins thread anymore, observing this Rosh Chodesh holiday has become rare, outside of Deformed Judaism. Still, it is brought in OC 417, starting with the Tur.
From the Yerushalmi, it would seem that this is a din that needs a minhag. In other words, a woman cannot choose to do this, it only has legitimacy if it is a minhag in her family from back in ancient times. As the Yerushalmi says, if they do it, it is a legitimate minhag, but only If they have the minhag
But in fact, Rav Ovadia Yosef says that the minhag still exists and should be respected. Women who choose to do this minhag should avoid heavy or tiring work. They can turn on a laundry machine, but they should arrange heavier jobs for a different day. This is based on a Pri Chadash, who says anyone can take this minhag upon themselves- פרי חדש' סי' תיז. A woman can wake up one Rosh Chodesh and tell her husband, "Guess who's cooking today, honey! I decided that I hold like the Pirkei D'Rebbi Eliezer and the Pri Chadash!" Which, of course, means they'll be eating out once a month.
UPDATE: My mother shetichyeh told me that she remembers clearly that the women of the Talmud Torah community in Kelm did not sew on Rosh Chodesh.
תדע לך שכל חודש וחודש חאשח מתקדשת וטובלת וחוזרת לבעלה והיא חביבה עליו כיום החופה כשם שהלבנה מתחדשת בכל ראש חודש והכל מתאוין לראותח כך האשה כשהיא מתחדשת בכל חודש בעלה מתאוה עליה וחביבה עליו כאשה חדשה
אור זרוע הלכות ראש חודש תנד
The Shaagas Aryeh, in his Turei Even on Megilla there, doesn't like any of this. He says that the Pirkei D'Rebbi Eliezer is, in his words, דברי אגדה בעלמא. This means that he thinks it's a nice story, but that is was intended to be non-halachic, an aggadic statement that has no halachic weight. So he proposes an entirely different explanation. He says that when the Beis Hamikdas was standing, not doing melacha on Rosh Chodesh was universal, because on the day that any person brings a korban, he may not do melacha (Tosfos, Ran and Rosh in Pesachim 50a, based on a Yerushalmi there, but see Rambam 6 Klei Hamikdash 10 that it's only derabanan). Since on Rosh Chodesh the Korban Musaf was brought on our behalf, we cannot do melacha. He brings a Yerushalmi that says that the only reason the Korban Tamid doesn't prohibit all the Jews from working every single day of the week is because of the passuk Ve'asafta deganecha, which allows melacha. He says that a remnant of this old minhag is the fact that there are four aliyos on Rosh Chodesh, which we don't allow on weekdays because of bittul melacha. This was instituted back when nobody worked on Rosh Chodesh, and stayed on the books even after the Churban Habayis.
So now: a question.
How can the Shaagas Aryeh just blow away a Yerushalmi and a Pirkei D'Rebbi Eliezer? "Just agadeta:"? It seems to be a little too dismissive, even by Shaagas Aryeh standards.
And this is how we come to the Kodshim part of this discussion.
The next part is succinct, but I think it's clear enough.
- Machtzis Hashekel provided the money from which community Korbanos were purchased.
- Women aren't chayav in Machtzis Hashekel.
- The Korban Musaf of Rosh Chodesh is a community Korban that is commemorated in Tefillas Musaf.
- Reb Akiva Eiger (Tshuvos 9 and OC 106) says that because women are not participants in the Korban Mussaf, they are not chayav to daven musaf. Unlike Shacharis and Mincha, Tefillas Musaf focuses exclusively on the Korban Musaf, and should only be said by a person who is chayav to participate in the Korban Mussaf. (This is also the opinion of the Tzlach in Brachos 26a, the beginning of the fourth perek, but for a different reason- because the davening of musaf is a zman grama and is not rachami, see Brachos 20b.)
- Additionally, some achronim (like the Steipler in Zvachim #3) say that all the Korbanos Tzibbur are zman grama and so women are doubly pattur from Korbanos Tzibbur.
- According to the Rambam (Sefer Hamitzvos) that the purpose of the chiyuv of building the Mishkan/Mikdash is to make it possible to do the Avodah, and if you say that their ptur from machtzis hashekel means they're unconnected to the primary avodah, the Avodas Korbanos Tzibur, why are women chayav to participate in the building of the mishkan (Rambam 1 Beis Habechira 12 and Minchas Chinuch 95:18)? If Mishkan= avodah, and women are pattur from avodah, then they should be pattur from Mishkan! Does it make sense that they should be pattur from the mitzvah and be chayav in the 'machshir'?
- The question arises only because of a failure to understand an enormous and fundamental conceptual difference of Avodas Hashem between women and men. The whole life story of women is that their greatest zechus is in supporting and enabling types of Avodas Hashem and mitzvos that they themselves are not chayav to do, like limud hatorah (hani nashi b'mai zachyan in Brachos 17a and Tshuvos Rashbash 324). This concept is emphasized in what they did in donating their jewelry to the mishkan.
- So for men, the Yomtov aspect of Rosh Chodesh stems from the Korban Musaf, as I said above from the Shaagas Aryeh, based on the first Tosfos in Makom She'nahagu, that the day that your special korban is brought is a Yomtov for you. For women, it can't stem from there, because they're pattur from the Mussaf. So their din Yomtov stems not from the Korban, but from their love for the mitzva of building the Mishkan, from their enthusiasm for seeing to it that a mitzvah gets done even when they themselves were not chayav to do the mitzvah.
- So for men, with the Churban Habayis and bittul of the korban, no more issur melacha. For the women, the yomtov was given without tna'im.
- Or, it is the men's nature of supporting the eigel that caused the churban. As far as women are concerned, we would still have the Beis Hamikdash, so the ptur melacha that stems from the Korban Musaf still applies.