On the Shabbos before Tishah B’Av, we read the haftarah of Chazon Yeshayahu, which contains harsh rebuke for the leaders of Yisrael, as well as its people. Let us examine the reason for this practice.
The Rambam in Hilchos Taanis states:
There are days on which all of Yisrael fast because of the tragedies that occurred on them, to arouse the hearts and to open up the paths of teshuvah, and serve to remind us of our evil actions, and of the deeds of our fathers which were akin to our actions today, causing these tragedies to befall both them and ourselves. For by remembering these matters we will return to proper conduct, as the pasuk states (Vayikra 26:40), “And they shall confess their sin and the sin of their fathers.”
The Chasam Sofer infers from the Rambam that the theme of the four fast days is not mourning but teshuvah. However, I have written elsewhere that in my humble opinion, it is clear that the four fasts relate to mourning. Many halachos are stated instructing us not to divert our thoughts from mourning on these days. Nonetheless, when we bring the destruction of our Beis Hamikdash to our attention and mourn over it, it is our responsibility to fix what went wrong and do teshuvah, as the Rambam writes, “Anyone who does not mourn as Chazal enacted is acting cruelly. Rather, he should be afraid and worry, and examine his actions and repent.” These words are particularly applicable to mourning over Yerushalayim and the Beis Hamikdash, for Chazal have stated, “Any generation in which it was not rebuilt is considered to have destroyed it.”
This is astounding. Any generation that does not merit the rebuilding of the Beis Hamikdash bears responsibility for the churban. For we do not only mourn over the churban of the Beis Hamikdash thousands of years ago, but for the Beis Hamikdash that was not rebuilt in our time. We fast so as to open our hearts to the path of teshuvah, as expressed by the Rambam.
The Maharsha in Bechoros relates that the twenty-one days between the seventeenth of Tammuz and Tishah B’Av correspond to the twenty-one days between Rosh Hashanah and Hoshana Rabbah. Just as the days from Rosh Hashanah to Sukkos are days of judgment and auspicious days for atonement from sin, so are the days from the seventeenth of Tammuz until Tishah B’Av days of judgment, repentance, and atonement.
Based on this assertion, the Maharsha explains the episode in which the elders of Athens brought two eggs before Rabbi Yehoshua ben Chananiah, one black and one white. He writes that the two eggs allude to these two sets of twenty-one days, as it takes twenty-one days for an egg to be formed. The black egg alludes to the twenty-one days between the seventeenth of Tammuz and Tishah B’Av, for it is customary for mourners to dress in black. The white egg alludes to the twenty-one days of atonement during the month of Tishrei, alluding to the pasuk, “If your sins will be as scarlet, they shall become white as snow.”
These days are not just days of mourning, but of introspection, repentance, and correction of our deeds, for if we are considered to have destroyed the Beis Hamikdash, it is our responsibility to rebuild it.
Therefore, the custom was established to recite Chazon Yeshayahu, so that we should repent, and correct our ways.
Excerpted from Rav Asher Weiss on Mo’adim – Bein Ha’metzarim