Maseches Taanis, Chapter 4, Mishnah 8 - the final mishnah of the maseches. After dealing with the sad days of the Jewish calendar, the mishnah turns to two of the most joyous days of all: "Lo hayu yamim tovim l'Yisrael k'chamishah asar b'Av u'k'Yom HaKippurim" - there were no festive days for Israel like the fifteenth of Av and Yom Kippur.
The mishnah will go on to describe how the daughters of Israel would go out on these days and present themselves for matchmaking. It is worth emphasizing that this is not the reason for the joy, but rather a result of it: since these days were days of joy to begin with, they were designated as the occasion for arranging matches. The Gemara lists a number of reasons for the joy of the fifteenth of Av.
The reasons for the joy of the fifteenth of Av:
The annulment of the prohibition against marrying between tribes - following the episode of the daughters of Tzelafchad, who received their father's portion in the Land, the members of their tribe were concerned that if they married into another tribe, the other tribes would inherit their portion. For this reason, the first generation that settled the Land was forbidden to marry from one tribe to another. This prohibition applied to that generation alone, and it was annulled on the fifteenth of Av.
The permitting of the tribe of Binyamin - in the wake of the episode of the concubine at Givah, the tribe of Binyamin was temporarily forbidden to marry into the congregation, and that prohibition was lifted on the fifteenth of Av.
The deaths of the generation of the wilderness ceased - it was decreed upon those who left Egypt that they would die in the wilderness and not enter the Land, and each year they would go down into graves. On the fifteenth of Av the dying ceased, and then they realized that the decree had come to an end.
The abolishing of Yeravam's guard posts - Yeravam ben Nevat separated the ten tribes from the rest of the Jewish people and sought to establish a separate capital. To that end he stationed guards to prevent people from going up to Yerushalayim to bring offerings and to be oleh regel. Hoshea ben Elah abolished these guard posts on the fifteenth of Av.
The burial of those killed at Beitar - this is the day on which permission was granted to bury those killed at Beitar, and in commemoration of this we recite the berachah of "HaTov V'HaMeitiv," the fourth berachah of Birkas HaMazon.
The completion of the cutting of wood for the altar - each year they would complete on this day the cutting of the wood for the arrangement on the altar, and the completion of the work was itself considered cause for joy.
The joy of Yom Kippur is self-understood: it is the day on which the sins of Israel are forgiven.
The custom of the daughters of Yerushalayim:
"Shebahen benos Yerushalayim yotzos b'chlei lavan she'ulin" - on these days they would go out in white garments, all of them borrowed. And the reason, in the words of the mishnah: "shelo l'vayesh es mi she'ein lo" - so as not to embarrass one who did not own such garments. They all borrowed from one another, so that it was impossible to know whose garment it was and who its owner was, and thus everyone was equal.
"Kol hakeilim te'unin tevilah" - all of these garments required immersion in a mikvah, since it was not known who was tahor and who was not.
"U'venos Yerushalayim yotzos v'choles bakramim" - they would go out and dance in the vineyards. And what would they say?
"Bachur, sa na einecha u're'eh mah atah borer lach" - young man, lift up your eyes and see whom you are about to choose as your match.
"Al titen einecha ba'noi" - do not set your mind on beauty.
"Ten einecha ba'mishpachah" - look at the lineage and at the family she comes from.
Support for this is brought from the verse in Mishlei: "Sheker hachen v'hevel hayofi, ishah yiras Hashem hi tis'halal" - grace is false and beauty is vain, but a woman who fears Hashem is the one worthy of praise. And it also says: "Tenu lah mipri yadeha vihaleluha ba'shearim ma'aseha" - it is her deeds that praise her in the gates.
"Tzena u're'ena benos Tziyon ba'melech Shlomo":
The mishnah brings an additional verse, from Shir HaShirim, which alludes to the joy of the Holy One, blessed be He, on these days: "Tzena u're'ena benos Tziyon ba'melech Shlomo ba'atarah she'itrah lo imo b'yom chasunaso u'v'yom simchas libo". And its explanation:
"Melech Shlomo" - this is not a reference to King Shlomo, but to the King to whom peace belongs, the Holy One, blessed be He.
"Imo" - an allusion to the entire Jewish people.
"B'yom chasunaso" - this is the giving of the Torah, and an allusion to Yom Kippur, on which the second luchos were given, which were the conclusion of the giving of the Torah.
"U'v'yom simchas libo" - this is the building of the Beis HaMikdash, which was dedicated on Yom Kippur in the days of Shlomo.
May it be rebuilt speedily in our days, amen.
With this we conclude our study of Maseches Taanis. I hope you will join us for the next maseches - Maseches Megillah.