The opening Mishna of Masekhet Megilla famously establishes that cities that were walled at the time Benei Yisrael first settled the Land of Israel celebrate Purim on the 15th of Adar, as opposed to other communities, which celebrate Purim on the 14th. And thus in Jerusalem, Purim is celebrated a day later than in other towns and cities.
Later (19a), the Mishna addresses the situation of a person who lives in one kind of city but happens to find himself on Purim in a different kind of city. The Mishna rules that if the visit is temporary, then an individual’s status is determined by his place of residence, not where he happens to be on Purim. For example, if a Jerusalemite is in a different city on Purim, but plans on returning to his home in Jerusalem, he observes Purim on the 15th, just as he would back home.
However, the Gemara cites Rava as drastically limiting the scope of the Mishna’s ruling, claiming that it refers only to somebody who plans to return home during the night of Purim. If a Jerusalemite is somewhere else on the night of the 14th of Adar, and remains there until daybreak, he must observe Purim on the 14th, even though he lives in Jerusalem and is visiting a different town only temporarily. Rava formulates this rule by saying, “Paruz ben yomo nikra paruz” – somebody who is in a “paruz” – a regular city, that was not walled at the time of the Israelite conquest of Eretz Yisrael – even for just one day is considered a resident of that city, and must celebrate Purim on that day.
Rava derives this principle from the verse in Megilat Ester (9:19) which refers to those living in regular cities as “ha-Yehudim ha-perazim ha-yoshevim be-arei ha-perazot” – “the Jews of the unwalled cities, who reside in the unwalled cities.” This verse is repetitious, Rava explained, to emphasize that even those who “reside” in an unwalled city for just the day of Purim are considered “residents” with respect to the Purim obligation, despite the fact that they plan on then returning to their home in a walled city.
It has been noted that the Purim observance differs in this regard from other halakhot, which depend on a person’s place of permanent residence. For example, a resident of Israel who temporarily visits the Diaspora during Yom Tov does not celebrate the additional day of Yom Tov observed in the Diaspora (although he must refrain from melakha in deference to the community he is visiting), and, according to the majority of poskim (notable exceptions notwithstanding), a Diaspora Jew who visits Israel on Yom Tov must observe both days, as he would back home in the Diaspora. (See Shulchan Arukh, O.C. 496:3, and Mishna Berura.) When it comes to Purim, however, even a temporary, one-day visit lends the visitor the status of a permanent resident.
Some have suggested that this halakha reflects one of the important themes of Purim, the notion that nothing is coincidental, that every situation we find ourselves in has great significance. Mordekhai expressed this idea to Ester in insisting that she approach Achashveirosh to appeal on the Jews’ behalf, rhetorically asking, “Who knows if you reached royalty for this very moment?” (4:14). More generally, the entire story of Purim is a series of seemingly coincidental events that we are to perceive as the workings of the mysterious Hand of Providence. And thus specifically on Purim, “paruz ben yomo nikra paruz” – wherever we happen to find ourselves is considered our “residence,” the precise place and circumstance where we belong. On Purim, we are to reinforce our belief that everything situation unfolds for a purpose, that we are meant to be in every circumstance we happen to find ourselves at any given moment. The place we happen to be on Purim is considered our “residence” – the exact location and situation that is right for us.
Like Ester, we occasionally end up in places and in settings that we never wanted and which we would have much preferred to avoid. One of the messages of the Purim story is that “you reached royalty for this very moment,” there is something we can achieve and accomplish under all circumstances, even those which we never planned and never imagined.