The Mishna in Ta'anis 4:8 states: Rabi Shimon ban Gamliel said "Israel has no days as festive as the 15th of Av and Yom Kippur...."

In order to understand the significance of the 15th of Av we will consult the Gemora, where we will find the explanations of why exactly this day is a day of happiness.

The Gemora in Ta'anis lists six reasons why the 15th of Av is such a festive day. It begins with the reason given by Rabi Yehudah in the name of Shmuel. The Torah tells us in Bamidbar 36:8-9 that "any unmarried woman who inherits property...shall marry one from a family of the tribe of her father's, so that...an inheritance will not pass from one tribe to another." This restriction prevented the transfer of the inheritance a woman received from her father to her husband's tribe permanently upon her death. On the 15th of Av, the Sages arrived at the conclusion, based on an understanding of a verse, that this restriction only applied to the generation that entered the land of Israel with Joshua. The lifting of this restriction was a cause of great joy, especially among women. Previously, if a woman was an heiress, she could only marry someone from within her tribe. Now, all women were free to marry any man from any tribe. Because of the joy that was experienced in that time, this date, the anniversary of that lifting of the restriction, is also a day of great joy.

The next reason the Gemora offers is that of Rav Yosef in the name of Rav Nachman. In Shoftim (Judges) 19-20, we find the incident of the "Pilegesh in Giv'ah." A man was traveling with his concubine (Pilegesh, in Hebrew) and servant back to his home. As evening approached, the group of travelers arrived in the city of Giv'ah, in the territory of the tribe of Benjamin, hoping to find a place to stay. Only one old man offered to put the group up.

He brought them to his home, and offered them and their donkeys food and drink. As the guests were refreshing themselves, wicked people from the city began banging on the door of the house, demanding that the old man send out the male guests from his house. The old man went out to the crowd, and tried to appease them by offering his own daughter and the man's concubine. He pleaded with them not to do anything disgraceful. The crowd took away the concubine. When she returned the next morning, after being assaulted, she collapsed and died on the old man's doorstep. In the morning, the man discovered his concubine was dead. He took her body with him back home. He then cut her body into 12 pieces, sending each tribe of Israel a piece, to inform them of the abomination that occurred.

The whole nation was in an uproar and disgusted by what had happened. Over 400,000 warriors from all tribes gathered to eradicate this evil. The group demanded from the tribe of Benjamin that the evil men of Giv'ah be turned over, but the tribe refused and joined with the inhabitants of Giv'ah to battle against the rest of the nation. On the first two days of the battle, the unified tribes suffered severe casualties. The tribes then offered sacrifices, prayed, cried, and fasted, asking Hashem for His assistance. They asked the Kohen Gadol what should be done. He responded that on the next day, the tribe of Benjamin would be delivered into the hands of the rest of the nation. That is what happened.

After this incident, the tribes swore that they would not let any man from the tribe of Benjamin marry their daughters. The people who made the oath felt much remorse over having to take such an action, as they were in essence cutting off a tribe from Israel. On the 15th of Av, it was established that the oath-takers had only intended for the oath to apply to themselves, and not to their children. Hence, on the 15th of Av, the tribe of Benjamin was permitted to "re-enter" the nation of Israel, and to have its sons' marry the daughters of any tribe. This was a cause for great happiness.

The third reason the Gemora gives is that of Rabi bar bar Chana in the name of Rabi Yochanan. As we noted in YomTov # 31, the adult Jews who departed from Egypt had a decree placed on them that they were to die before their children entered the land of Israel. The nation knew that the deaths related to this decree occurred annually on the 9th of Av. Each year, every man in the age group destined to die would dig a grave for himself and lie down in it on the eve on the 9th of Av. All those who remained alive come the close of the 9th of Av would get up, and repeat the same actions the next year. In the 40th year, everyone arose. Seeing that no one had died, they thought that they might have erred in their calculation of the date, so they returned to their graves every night until the night of the 15th. On the 15th, they saw the full moon which indicated that their calculations were correct, and still no one had died. The decree was over, and there was cause for celebration.

Furthermore, the Gemora tells us that as long as those destined to die were still alive, the Divine Communication between Hashem and Moshe was on a lower and less personal level, to the extent that the Gemora considers it "no Divine Communication." Once the 15th of Av passed and it was confirmed that the decree was no longer, Hashem resumed speaking to Moshe as he had before the enactment of the decree. As this communication was for the benefit of Israel, the day it returned was a day of rejoicing and celebration.

Check out all of the posts on The Three Weeks: 17 Tammuz - 9 Av Mourning the Destruction. Head over to http://www.torah.org/learning/yomtov/ to access the YomTov Page. Then click on the icon for the holiday of your choice.