When the fast of Shivah Asar BeTammuz or Tishah BeAv falls on a Shabbos, the fast is nidcheh, “set aside” or “pushed off,” until the following day.

The Previous Rebbe related1 that one year when Shivah Asar BeTammuz fell on a Shabbos, his grandfather, the Rebbe Maharash, was highly elated and mentioned a number of times that the Shabbos is called “nidcheh.” He concluded: “Would that it [the fast] be truly nidcheh [through Mashiach’s arrival].” Added the Previous Rebbe, “and transformed into joy and gladness.”

The connection between “temporary nidcheh” and “permanent nidcheh” is as follows. When a fast is nidcheh, the fast’s stringency is considerably lessened.2 As such, the tempered “temporary nidcheh” points the way to the “permanent nidcheh” of the Time to Come.

This will be better understood by prefacing the classical dispute in the Gemara concerning nidcheh:3 When Tishah BeAv falls on a Shabbos, it is Rebbe’s (R. Yehudah HaNasi) opinion that since the fast must in any event be nidcheh until after Shabbos, it should be entirely nidcheh that year. The Sages, however, maintain that the fast is merely nidcheh to Sunday. What is the basis for their argument?

Our Rabbis explain4 that there are two aspects to a fast: the application of the name of the fast as it relates to the fast day; the application of the laws and obligations of the fast as it relates to the individual.

Accordingly, we may say that the dispute between Rebbe and the Sages revolves around the status of the “nidchehShabbos day:

According to Rebbe, nidcheh sets aside the “name” as well — Shabbos cannot be termed a “fast day” at all. Since it ceases to be a fast day, Rebbe maintains that the fast cannot possibly carry over to the next day. According to the Sages, the nidcheh aspect applies only to fulfilling the fast day laws, the name of the day — the fact that it is a “fast day” — however, remains.

But how can the term “fast day” apply to Shabbos, when it is expressly forbidden to fast on Shabbos?5

The explanation is as follows. A fast day is distinguished in that it is considered “a day desirable by G‑d.”6 Although this applies primarily to fasts for repentance and atonement,7 while Tishah BeAv is a fast of mourning over the tragic events that befell the Jewish people on that day, still, even the fast of Tishah BeAv incorporates the theme of repentance.

Thus the Rambam writes8 concerning the fasts that commemorate tragic events in Jewish history that they too are meant “to rouse the hearts, to open the pathways of repentance...; by remembering these days we will return to doing good deeds.…” Hence, even so mournful a fast as Tishah BeAv contains the element of repentance. Consequently, it too is considered a propitious day, “a day desirable by G‑d.”

In light of the above, we can well understand that when Tishah BeAv falls on Shabbos, a day in which “there is no sadness therein,”9 the prohibition of actually fasting on that day does not negate the quality of the day remaining “a day desirable by G‑d.”

This also helps explain a crucial aspect of the future status of these mournful fast days: In the era of Mashiach these days will not only cease to be fast days, they will actually be transformed into Yomim Tovim and days of gladness and rejoicing.10

The nullification of these fasts in the Time to Come is understandable. Since they are a remembrance of the travails that befell our ancestors, then with the cessation of the memory of these travails through the Redemption, the fasts will cease as well. But why will they be transformed into days of gladness and rejoicing? How does gladness and rejoicing enter the picture?

According to the above, the matter is eminently clear: The main aspect of a fast day is not affliction, but that it is “a day desirable by G‑d.” Only, that during the time of exile, when our sins that caused the exile have not yet ceased, the manner of utilizing and approaching the special qualities of this day can only be through fasting and afflicting the body, serving as it does to arouse even a coarse person to repentance.

With the arrival of Mashiach, when “the spirit of impurity will depart from the earth,”11 there will be no place for afflicting the body; all that will remain is the aspect of increasing our Divine service in a manner of joy and gladness of heart.

Thus, these intrinsically desirable days will then be “truly nidcheh” from days of fasting and sadness, and be transformed into “days of joy and gladness.”

Based on Likkutei Sichos, Vol. XXXIII, pp. 156-163.