Likkutei Sichos, Vol. 19 Shabbos Nachamu

The Context:

There were several dates when specific families donated wood to the Temple and observed that day as a private holiday. One of those days was the 20th of Av. (Taanis 26a) It was possible that these days would coincide with Shabbos. When that occurred, the family would postpone the donation to Sunday, and not advance the observance to Friday. (Megillah 5a)

In two locations, Rashi seems to offer divergent explanations for this practice. In his commentary to tractate Megillah, he explains that the family could not advance their offering to Friday because the time-frame of their obligation had not yet arrived. When it did arrive, on Shabbos, they could then wait until the first opportunity to fulfill their obligation, on Sunday.

In his commentary to the Rif, however, he explains this differently. The previous family’s obligation extends until the onset of the next family’s obligation. The family whose obligation fell on Shabbos cannot advance their offering to Friday, because they would be interfering with the previous family’s time-frame.

The Question:

These explanations seem to contradict one another. The implication of the second explanation is that if the previous family would allow the current family to advance their offering to Friday, then that would be permissible. It is only because we assume that the previous family does not want its time cut short that we defer the current family’s offering to Sunday. But Rashi’s first explanation (in Megillah) implies that under no circumstances can the family advance their offering to Friday, because their obligation has not yet begun.

The Explanation:

The obligation to bring the wood offering was a consequence of the family’s vow. When they made that pledge originally, it binded them for all future generations. When deciding the legal boundaries of a vow, we consider the mindset of the person at the time of the vow. In our scenario, when a family vowed to bring the wood offering, they knew it was common that the day could coincide with Shabbos, and took it as obvious that the previous family would want to use their entire time-frame for their offerings. Therefore, when the vow was originally made, it was made with the understanding that if the day fell on Shabbos, their obligation would be moved to the following day, Sunday.

Both of Rashi’s explanations, therefore, are compatible. When he says that, on Friday, the time for the offering had not yet arrived, he is referring to the fact that implicit in the vow was the stipulation that when the day fell on Shabbos, the family would move to Sunday to accommodate the previous family, as Rashi detailed in his commentary to the Rif.

This all applies to a situation where one family’s vow invades the time of another family’s. That is when we defer their obligation to Sunday. But when no such conflict exists, there is no reason to defer one’s commitment to later. So, for example, when a yahrzeit falls on Shabbos, there is no reason to defer a vow of charity to Sunday. Rather, one can advance their charitable giving in honor of the yahrzeit to Friday, for there is no reason to delay the fulfillment of a mitzvah.