The Talmud relates that on the 17th of Tammuz the first Tablets were broken, and then years later on the same day the walls of Yerushalayim were breached. It is this latter occurrence which places the 17th of Tammuz among the fast days observed in commemoration of the destruction of the Beis HaMikdash. However, the inner meaning of this day is not limited to mourning. Fasting is also a means whereby the tragic event is eliminated.
From the Rebbe’s explanations:
– On an obvious level, a fast day is undesirable. The suffering endured on a fast is not appreciated. Nevertheless, the inner dimension of a fast is good, as the prophet states:
“It is a day of will unto HaShem” (Yeshayahu, 28:5; “Tania”, “Igeret HaTeshuvah”, chapter 2).
This contrast is openly expressed in regard to the Seventeenth of Tammuz. On an obvious level, it is associated with negative factors, the breaching of the walls of Jerusalem which led to destruction and exile. Nevertheless, its inner, essential quality is good.
This is even alluded to in the date itself, for 17 is numerically equivalent to the word טוב – “good” in Hebrew.
This points to the intent of the exile, that it should lead the Jews to the Era of the Redemption.
This contrast is also evident in our Sages’ interpretation of the verse quoted by the Rambam as the prooftext for the concept that the nature of the fasts will be transformed in the Era of the Redemption:
“The fast of the fourth month (17 Tammuz), the fast of the fifth month (Tisha B’Av), the fast of the seventh month (Tzom Gedalya), and the fast of the tenth month (the 10th of Tevet) will be [days] of rejoicing, [days] of happiness, and holidays for the House of Yehudah; and they shall love truth and peace…” (Zechariah 8, 19).
In the Talmud, our Sages comment:
These days are called “fasts” and they are called “[days] of rejoicing” and “[days] of happiness.” How so? When there is peace, they will be “[days] of rejoicing” and “[days] of happiness.” When there is no peace, they will be “fasts” (Rosh Hashanah 18b).
Thus, the days of fasts have two dimensions. All we see in the era of exile is the unfavorable dimension. The inner good is hidden. However, in the Era of the Redemption, it will be revealed. The days of mourning will become days of rejoicing — may it be even before the conclusion of this day.
Excerpted from the Rebbe’s talk on Shabbat Parshat Balak, 17th Day of Tammuz, 5751 (free translation).