Ma'aser Sheni, Chapter 2, Mishnah 2. The Mishnah continues to deal with the laws of a fourth-year vineyard, and teaches that even though a fourth-year vineyard, like Ma'aser Sheni, can be redeemed - redeeming it with money and bringing the money up to Jerusalem - an enactment and decree was made that the fruits of the fourth year themselves should be brought up to Jerusalem. In any place located within a distance of one day's travel from Jerusalem, it was decreed that the fruits themselves be brought up, at the very least the grapes, and be eaten in Jerusalem rather than redeemed. The Mishnah describes that enactment and what happened as a result of it.
The Wording of the Mishnah and the Reason for the Enactment:
The Mishnah opens: "Kerem revai hayah oleh liYerushalayim mahalach yom echad l'chol tzad" - the enactment was that the fruits of the vineyard's fourth year, those very grapes, be brought to Jerusalem from any place located within a distance of one day's travel from Jerusalem in any direction. The reason for the decree is explained in the Gemara in Beitzah: "in order to adorn the markets of Jerusalem with fruit." That was the purpose of the enactment, and therefore a radius of one day's travel was sufficient and no more than that was required.
The Boundaries of the Decree:
The Mishnah continues and defines the borders of that region: "V'eizeh hatechumah" - what is the boundary:
"Eilat min hadarom" - and this is not the Eilat of our own day, which is certainly farther away than one day's travel.
"V'Akrabah min hatzafon" - Akrabah in the north.
"Lod min hama'arav" - Lod in the west.
"V'Yarden min hamizrach" - the Jordan River in the east.
The Annulment of the Enactment and the Condition Attached to It:
Since the entire purpose of the enactment was "in order to adorn the markets of Jerusalem with fruit," the Mishnah continues: "Umisherabu haperos hiskinu sheyeheh nifdeh samuch lachomah" - when fruit became plentiful in the markets of Jerusalem, they established a rule returning to the original law, that the fruits of the vineyard may be redeemed with money, even in a place right next to the walls of Jerusalem. That enactment was no longer needed.
The Mishnah adds, however: "Tenai hayah hadavar" - when they ruled that there was no longer a need to bring the fruit itself, they attached a condition, "she'amru shekesheyirtzu yachzor hadavar lechmos shehayah" - that whenever they wish, they can restore the matter to what it was, and bring the fruits themselves to Jerusalem from within a day's travel, and this again "in order to adorn the markets of Jerusalem with fruit."
The View of Rabbi Yosi:
Rabbi Yosi has a different tradition regarding the way this change came about. In his view, the change and the condition attached to it were not made because fruit became plentiful and there was no longer a need to adorn the markets of Jerusalem; rather, they occurred at the time of the destruction of the Beis HaMikdash: once the Beis HaMikdash was destroyed, they no longer wished to adorn the markets of Jerusalem. At that time the change was made, and a condition was stipulated that when the Beis HaMikdash would be rebuilt, speedily in our days, the matter would return to what it had been - to adorn the markets of Jerusalem with fruit.
A Side Note - The Order of Events in the Days of Mashiach:
It is worth noting several fascinating points about this Mishnah. In the Yerushalmi on this Mishnah, the chronological order of events in the days of Mashiach is described differently from the way the Rambam presents it at the end of Hilchos Melachim. The Rambam writes that the King Mashiach will build the Beis HaMikdash, whereas according to the Yerushalmi the Beis HaMikdash will be rebuilt before the coming of Mashiach, prior to the reestablishment of the kingdom of the house of David.
In this connection, and in connection with additional questions that the Tosafos Yom Tov addresses here, he foresees that according to the Yerushalmi and according to this Mishnah, events will unfold as follows: the Beis HaMikdash will be built, and we will still not necessarily want to adorn the markets of Jerusalem with fruit, since the kingdom of the house of David will not yet have been restored, and to a certain extent we will still be under the rule of foreign governments even after the building of the Beis HaMikdash - similar to the situation when the Second Beis HaMikdash was built. And in our times it is not so hard to imagine such a thing happening.
In summary: In this Mishnah we learned the enactment to bring the fruits of a fourth-year vineyard themselves up to Jerusalem from within one day's travel in every direction, whose reason was "in order to adorn the markets of Jerusalem with fruit"; the boundaries of that region - Eilat in the south, Akrabah in the north, Lod in the west and the Jordan in the east; the annulment of the enactment once fruit became plentiful, and the condition stipulated that the matter would be restored to what it had been whenever they wish; Rabbi Yosi's tradition that the change occurred at the time of the destruction; and finally the side note regarding the order of the building of the Beis HaMikdash and the return of the kingdom of the house of David.