There never were in Israel greater days of joy than Tu B’Av and Yom Kippur. On these days the daughters of Jerusalem used to walk out in white garments which they borrowed in order not to put to shame any one who had none …

The daughters of Jerusalem came out and danced in the vineyards exclaiming at the same time, “Young man, lift up your eyes and see what you choose for yourself. Do not set your eyes on beauty but set your eyes on [good] family.” As it says, “Grace is deceitful, and beauty is vain; but a woman that fears the lord, she shall be praised.” (Ta’anit 26b)

[This is the concluding Mishnah of the tractate of Ta’anit, which deals with fast days. The previous Mishnah had taught the laws of Tisha B’Av. Now the Mishnah continues to the next day of importance in the Jewish calendar, Tu B’Av.]

I can understand the Day of Atonement, because it is a day of forgiveness and pardon and on it the second Tablets of the Law were given. But what happened on the 15th of Av? (Ta’anit 30b)

[Archeo-agronimists report: The grape harvest in the Land of Israel began around the time of Tu B’Av and ended by Yom Kippur. Is this why the young women danced in the vineyards?]

Rabba ben Bar Chana said in the name of Rabbi Yochanan: “It is the day on which the generation of the wilderness ceased to die out.”

Rabba and Rabbi Yosef both said: “It is the day on which [every year] they stopped chopping down trees for the altar.”

Rabbi Eliezer the elder said: “From Tu B’Av onward, the strength of the sun grows less and they no longer chopped down trees for the altar, because they would not dry [sufficiently].”

The Midrash describes the first Tu B’Av ever celebrated:

Rabbi Abin and Rabbi Yochanan said: “It was the day when the grave-digging ceased for those who died in the wilderness.”

Rabbi Levi said: On every eve of the 9th of Av, Moses used to send a herald throughout the camp and announce, “Go out to dig graves”; and they used to go out and dig graves in which they slept. The following day he sent out a herald to announce, “Arise and separate the dead from the living.” They would then stand up and find themselves in round figures: 15,000 short of 600,000.

In the last of the 40 years, they acted similarly and found themselves in undiminished numerical strength. They said, “It appears that we erred in our calculation”; so they acted similarly on the nights of the 10th, 11th, 12th, 13th, and 14th of Av. When the moon was full they said, “It seems that the Holy One, blessed be He, has annulled that decree from us all”; so they proceeded to make [the 15th] a holiday.