The numbers three and seven occur well over a hundred times in Judaism and even more in other cultures, as do their combination, the number ten, including on holy days. The fast day of Tisha b’Av, meaning the ninth day of the Hebrew month Av, seems to be an exception – but is it an exception? Tisha b’Av begins in 2023 on the evening of July 26 and continues on the 27th.
The number seven symbolized completeness to many ancients. They saw it in lots of places. For example, they felt the body was composed of seven parts, two eyes, two ears, a head, the upper and the lower body. Even heaven had seven, the number of planets they saw.
In Judaism, Ibn Ezra also interpreted seven as a symbol of completeness. It was a good symbol. But, he saw three as “bad because it is half” (or, more precisely, close to half) of seven. It is the turning point to the change that will reach its climax with seven. Thus, in Genesis 34:25, the people of Shechem were sickest on the third day after their circumcision. The idea of seven signifying positive completeness is also the view of other writers, such as S. R. Hirsch.
Baruch Epstein agrees as well. He states that everything becomes complete with seven. Thus, a person naturally only feels absolute joy after a seven-day celebration, as in the seven days of a wedding celebration and the seven days of Passover and Sukkot. Similarly, he thought that mourning can only be complete and cathartic if a person has seven days of strict mourning, called shiva.
Thus, it is possible that the word sheva, “seven,” is related to sova. The latter means satisfaction and completeness, as in eating until a person is satisfied. An example is I Chronicles 23:1, which states that David “was old and sova in days.”
The holidays of Chag Hamatzot (Passover) and Sukkot, happy times, last seven days.
So, too, are fast days, despite recalling calamities.
The fast of Tisha b’Av is connected to seven. It commemorates the destruction of the First and Second Temples. The Babylonians destroyed the First Temple on the seventh month of Av, according to II Kings 25:8–9, and the tenth of Av, according to Jeremiah 3:12, in 586 B.C.E. The Tosephta Ta’anit 4:10 and the Babylonian Talmud, Ta’anit 29a, explain the discrepancy: the outer walls were demolished on the seventh and the Temple itself on the tenth. In any event, we again see the numbers seven and ten.
The Romans destroyed the Second Temple on the tenth of Av in 70 C.E., according to the historian and Jewish general Josephus. Josephus was present at the occurrence. But several centuries later, the Babylonian Talmud, Ta’anit 29a, gives the date as the ninth of Av. Thus according to Josephus, at least we have another seven (three plus seven).
Why was a fast established on the ninth for destroying the First and Second Temples? It is possible that the rabbis did not want to use seven because this number is associated with completeness, creation, the Sabbath, and with joy, and the rabbis did not want to use seven and give the impression that Judaism was utterly destroyed and that there was joy connected to the event. Eight may not have been chosen since, as shown shortly, eight was seen as a symbol of a new beginning, and the Temple destruction ended an era. Similarly, ten may have seemed inappropriate because, as indicated earlier, it is made up of seven and three, the two numbers connected with completeness.
It is also possible that the rabbis did not want to have the fast of Av on the tenth because the tenth would remind the Jew of the other fast of the tenth, Yom Kippur, and they did not want the Jews to compare both days. The fast of Av is considered an enormous and total calamity. On the other hand, Yom Kippur has positive elements. During Temple days, the afternoon of Yom Hakippurim, the biblical name, was a happy time when young boys and girls would meet and dance. Additionally, on Yom Kippur, one can seek forgiveness for past misdeeds.
The remaining three minor fasts are associated with the number seven or its three and ten derivatives. The Fast of Gedalia occurs on the third of Tishrei. The fast of Asarah b’Tevet is on the tenth. The fast of Shiva Asar b’Tammuz is on the seventeenth, which is seven and ten.
If seven symbolizes completeness, then eight denotes the beginning of something new. A male child is circumcised on the eighth day after seven days of life. Similarly, the holiday of Shemini Atzeret occurs after the completion of the seven days of Sukkot. The rabbis conceive it as a renewal of a relationship with God.
Although Tisha b’Av, the ninth day of the month Av, appears at first blush to be an exception to the three and seven usages, it is possible that it is no exception. It may be seen as three times three. This multiple may have been chosen because three, as previously stated, is close to half of seven and signifies incompleteness and difficulty, such as Abraham traveling three days to sacrifice Isaac in Genesis 22. Perhaps three times three indicates that this day commemorating the destruction of the two temples is very sad, a three times multiple of sadness.
 See Israel Drazin, Maimonides and the Biblical Prophets, Gefen Publishing House, 2009, “The Significance of the Number Seven,” pages 277-303.
 Commentaries to Exodus 3:15; Leviticus 22:27, 23:24, 26:18; Numbers 23:1; and Deuteronomy 28:7.
 Commentary to Leviticus 12:2, 3.
 Tosaphot Berakhah, book one, pages 87–89, and Mekor Barukh, part 3, chapter 26.
 Wars 6:249–250.
 Yom Hakippurim was a day when the high priest would bring offerings and atone for his misdeeds, those of his family, and the nation. When the temple was destroyed and sacrifices ceased, Yom Hakippurim, which is plural since it dealt with many people, could no longer be observed. The rabbis invented Yom Kippur, singular, a day when individuals, not the High Priest, would fast and consider their own misdeeds and resolve to improve. See Israel Drazin, Mysteries of Judaism, Gefen Publishing House, 2014, “Yom Kippur: A Holiday the Romans Destroyed,” pages 16-18.
 S. R. Hirsch, ibid, note 3.