Look to the future for that’s where you’ll spend the rest of your life TB Megillah 2

The Megillah clearly states that Purim is celebrated on the 14^th day of Adar for the Jews of the provinces and on the 15^th day of Adar in Shushan. “The rest of the Jews, those in the king’s provinces, likewise mustered and fought for their lives. They disposed of their enemies, killing seventy-five thousand of their foes; but they did not lay hands on the spoil. That was on the thirteenth day of the month of Adar; and they rested on the fourteenth day and made it a day of feasting and merrymaking. (But the Jews in Shushan mustered on both the thirteenth and fourteenth days, and so rested on the fifteenth, and made it a day of feasting and merrymaking.)” (Esther 9:17-19)

The Mishnah on today’s daf TB Megillah 2 codifies the dates to celebrate Purim on the 14^th or the 15^th day of Adar; however, the rabbis added three more days when the Megillah could be read. “The Megilla is read on the eleventh, on the twelfth, on the thirteenth, on the fourteenth, or on the fifteenth of the month of Adar, not earlier and not later. The mishna explains the circumstances when the Megilla is read on each of these days. Cities [kerakin] that have been surrounded by a wall since the days of Joshua, son of Nun, read the Megilla on the fifteenth of Adar, whereas villages and large towns that have not been walled since the days of Joshua, son of Nun, read it on the fourteenth. However, the Sages instituted that the villages may advance their reading to the day of assembly, i.e., Monday or Thursday, when the rabbinical courts are in session and the Torah is read publicly, and the villagers therefore come to the larger towns.” (Sefaria.org translation, see the rest of the Mishnah how the Megillah could be read on the 11^th, 12th, or 13^th of Adar)

Nevertheless this rabbinic leniency only applies “At a time when the years are established properly and the Jewish people dwell securely in their own land.” (Sefaria.org translation) Since these two requirements are not applicable today the Gemara teaches “Rabba bar bar Ḥana said that Rabbi Yoḥanan said: This is the statement of Rabbi Akiva, the unattributed. However, the Sages said: Nowadays, since people look (וּמִסְתַּכְּלִין בָּהּ ) to the reading of the Megilla, one may read the Megilla only in its designated time.”  (Sefaria.org translation) Today all Jewish communities whether in the Diaspora or in Israel read the Megillah on the 14^th day of Adar with the exception of cities who were surrounded by wall since the days of Joshua (there really aren’t that many especially where Jewish community can be found).

What is the meaning of “since people look (וּמִסְתַּכְּלִין בָּהּ )?” According to Rashi, the fear is that people will celebrate Passover on the wrong date. Everybody knows that Passover is exactly 30 days after Purim. If people hear the Megillah reading on the 11^th, 12^th, or 13^th of Adar, and calculate 30 days forward to determine Passover, they will begin Passover too early and end it before it is over. Everybody who studied massekhet Pesakhim with me knows how terribly wrong that would be. The Rif understands that it is the poor people who are looking. The poor know on Purim we give tzedakkah to them, matanot le-evyonim (מתנות לאביונים) after the Megillah reading so that they may rejoice appropriately. They will feel distressed when these gifts are not forthcoming on the earlier Megillah reading. Rebbeinu Efraim explained the phrase in a similar manner. If the poor would receive their gifts early, they may spend the money unwisely before the holiday and not have the means to celebrate Purim appropriately. Rav Hai Gaon, based on his version of מִסְתַּכְּלִין, feared that the Gentiles in his day will see the Jews excessively rejoice over several days and be incited to persecute and endanger the Jews.