As we learned on yesterday’s daf, following the destruction of the Temple, Rabban Yohanan ben Zakkai established Rabbinic ordinances whose purpose was to remember the Mikdash. The Mishna on our daf discusses how his rulings affected the holiday of Sukkot.
The pesuk that commands us to take the arba minim on Sukkot (Vayikra 23:40) is enigmatic. It describes the mitzva as commanding us to take the four species on “the first day [of the holiday]” and then continues that you should “rejoice before God for seven days.”
The Mishna teaches that originally the halakha was that the arba minim were taken one day in all places (medina), and seven days in the Beit HaMikdash (“before God”). There is a difference of opinion amongst the rishonim regarding the definition of mikdash in this case. Rashi, the Ritva and others explain that any place outside of the Temple – including the Old City of Jerusalem – is considered medina and the lulav is not taken there. The Rambam rules that the holiness of the Temple extends to the entire city and therefore all of Jerusalem is considered mikdash for this purpose. The Jerusalem Talmud is clear on this point, in agreement with the Rambam. Thus it is possible even today that there is a biblical obligation to take the arba minim when visiting the Old City of Jerusalem.
This rule was changed with the destruction of the Temple. At that time Rabban Yohanan ben Zakkai instituted a Rabbinic decree obligating the lulav and etrog to be taken for all seven days of the holiday, zekher la-mikdash – as a remembrance of the Temple and its unique rule.
The Meiri points out that Rabban Yohanan ben Zakkai did not actually establish the mitzva for all seven days as in the Temple, since at least one of the days will fall out on Shabbat, when, nowadays, the lulav is not taken. Nevertheless the point is that the obligation, as it was practiced in the Beit HaMikdash, is remembered.