Másodnapi Sávuot

There are places where the messengers [sent out for] Nisan would arrive [in time for the celebration of Pesach], but the messengers [sent out for] Tishrei would not arrive [in time for the celebration of Sukkot]. According to [the letter of] the law, it would have been appropriate for them to observe Pesach for one day, since the messengers reached them and informed them when Rosh Chodesh had been established, and for them to observe Sukkot for two days, since the messengers had not reached them. Nevertheless, so that there would be no difference between the festivals, the Sages instituted the ruling that two days were celebrated [for all holidays] in all places that were not reached by the messengers for Tishrei. [This includes] even the festival of Shavuot.

It was further related that Rabbi Yoḥanan used to proclaim: Anywhere that can be reached by the messengers who go out in Nisan in time to inform the people when to observe Passover, but cannot be reached by the messengers sent out in Tishrei, let them also observe the festival of Passover for two days. The messengers did not travel on Rosh HaShana or Yom Kippur, and therefore they could travel three days further in Nisan than in Tishrei. The Sages instituted that two days must be observed in Nisan as a rabbinic decree due to Tishrei, for if they observe Passover for only one day, they will come to observe Sukkot for one day as well, and this they are not permitted to do.

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