If the 17th of Tammuz falls on a Shabbat, the fast of this day is observed the next day, the 18th of Tammuz (on Sunday).
The Rebbe reveals:
– On an obvious level, a fast day is undesirable. The suffering endured on a fast is surely not pleasurable, nor appreciated. Nevertheless, the inner dimension of a fast is good, as the prophet states, “It is a day of will (et ratzon) unto G‑d.”
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 the destruction of the Beis HaMikdash. Nevertheless, its inner, essential quality is good. This is even alluded to in the date itself, for number 17 is numerically equivalent to the word טוב – “good”. This points to the intent of the exile, that it should lead the Jews to the Era of the Redemption.
Indeed, in microcosm, we see such a transformation when a fast falls on Shabbos. The date is characterized by Shabbos pleasure instead of fasting. Thus there are two dimensions to such a day: the negation of the undesirable elements associated with a fast and the emphasis on the inner positive nature of the fast which is openly revealed on Shabbos.
The connection to the Redemption also relates to Shabbos which is a foretaste of “the era which is all Shabbos and rest for eternity.” Moreover, the mitzvah of delighting in the Shabbos by partaking of material delicacies is also paralleled by “the feast which the Holy One, blessed be He, will make for the righteous in that future era.” Although the different elements of that feast surely have spiritual connotations, that feast will be an actual physical meal. For, as Chassidus explains, the ultimate reward of the Era of the Redemption will not be on the spiritual plane — like the reward experienced by the souls in Gan Eden where they are not enclothed within a body. Rather, it will be experienced within this material world, as the souls are enclothed within the body.
Thus when a fast day falls on the Shabbos and we fulfill the mitzvah of taking pleasure in material delights —
indeed, that mitzvah should be fulfilled to a greater extent on such a Shabbos than on other Shabbasos during the year to show that there is no room for sadness on such a day —
we have a heightened sensation of the positive dimension of the fast day which will be experienced in the Era of the Redemption.
Based on the Rebbe’s talk on Shabbat Parshat Balak, 17th Day of Tammuz, 5751 (1991).