Question: There would be no point in establishing the 3rd of Tishrei as a festive day for when the Beis ha'Mikdash is standing, as it would anyway be festive as it is the fast of Gedalyah (which is a festival in the time of the Beis ha'Mikdash standing)!?

Answer (Rav): The point would be to prohibit the preceding day for fasting.

Question: The preceding day would anyway be forbidden for fasting, as it is the day after Rosh Chodesh!?

Answer: Rosh Chodesh is a d'Oraisa festival, which does not need the reinforcement of prohibiting fasting on the following day:

(Beraisa): The festive days listed in Megilas Taanis are forbidden for fasting on the days preceding and following them as well.

With Shabbos and Yom Tov, one may fast on the preceding and following days.

The reason is that the latter are d'Oraisa, which don't need reinforcement, whereas the former are d'Rabanan and need reinforcement.

Question: The preceding day would anyway be forbidden for fasting, as it is the day before the day when Gedalyah was killed!?

Answer (R. Ashi): The fast of Gedalyah is Divrei Kabalah (from Nevi'im) which is like a d'Oraisa fast in that it does not need reinforcement.

Question (R. Tuvi bar Masna): We see that Megilas Taanis was not annulled:

The government decreed that Jews may not study Torah or circumcise their sons and that they must transgress Shabbos.

Yehudah ben Shamua and his friends asked advice from a princess who was familiar with all the prominent Romans.

She advised them to make a demonstration at night.

They did so, and said, "We are all brothers, why do you persecute us?"

The decrees were annulled, and that day (the 29th of Adar) became a festival.

If Megilas Taanis was annulled, how could they make a new such festive day?

Answer: This day was only made into a festival for when the Beis ha'Mikdash is standing.

Question: Yehudah ben Shamua was a disciple of R. Meir, who lived after the Beis ha'Mikdash:

(Mishnah): If a glass vessel (which became Tamei) was punctured (to make it Tahor) and the hole filled with lead;

(R. Shimon ben Gamliel citing Yehudah ben Shamua citing R. Meir): It reverts to its Tum'ah.

(Chachamim): It is Tahor.

Answer: Whether Megilas Taanis was annulled is a dispute between Tannaim in a Beraisa:

(R. Meir): The days listed in Megilas Taanis are forbidden for fasting whether or not the Beis ha'Mikdash is standing.

(R. Yosi): They are only forbidden for fasting when the Beis ha'Mikdash is standing.

The Halachah is that these days were annulled.

The Halachah is that these days were not annulled.

Question: This is a contradiction!?

Answer: It is only Chanukah and Purim that were not annulled.

Question: Since messengers were sent out for Rosh Chodesh Elul, why do they need to be sent out for Tishrei?

Answer: In case Elul became a full month.

Question: R. Chanina bar Kahana citing Rav stated that we do not find that Elul has ever been a full month since the time of Ezra!?

Answer: "We don't find it" because it was never necessary; but if necessary, it would be made a full month.

Question: If that were to happen, people in the Diaspora would keep Rosh Hashanah on the wrong day!?

Answer: Better for that to happen than for the festivals to be kept on the wrong days.

This can be deduced from the Mishnah's statement that messengers were sent out for Tishrei to ensure that the festivals are kept at the correct time.

The Mishnah does not state that, in the event of a leap year, messengers would be sent out for Adar Sheni because of Purim.

We see that the Mishnah does not follow Rebi:

(Rebi): In the event of a leap year, messengers would be sent out for Adar Sheni because of Purim.

Question: Perhaps they are arguing about whether all the mitzvos of Adar Sheni apply in Adar Rishon (and therefore one can fulfill one's obligations then)?

Answer: All agree that the mitzvos do not apply in Adar Rishon; the dispute is over the length of Adar Rishon, as in a Beraisa:

(Tana Kama): Adar Rishon is thirty days.

(R. Shimon ben Gamliel): Adar Rishon is one month (assumed to mean 29 days).

Question: In either case, they know when Adar Sheni will arrive?

Answer (R. Papa): The view that it is one month holds that it can be 29 or 30 days (and messengers would need to be sent).

R. Yehoshua ben Levi testified that the Jerusalem community would make the 30th day of each Adar into the first of the next month.

We see that both months would always be abridged, unlike the following view:

(R. Nachman bar Chisda): R. Simai testified in the name of Chagai, Zacharyah and Malachi that both or either months of Adar could be made full or abridged.

Thus was the custom in the Diaspora.

Rav's view was cited that Adar Rishon was always full and Adar Sheni always abridged unless a message was sent from Eretz Yisrael otherwise.

A message was sent to Mar Ukva that the Adar closest to Nisan is always abridged.

Question (R. Nachman): We see otherwise:

(Mishnah): The witnesses of the moon for the months of Nisan and Tishrei can transgress Shabbos.

That makes sense if the months were sometimes full and sometimes abridged.

But if the Adar closest to Nisan was always abridged, why should they be allowed to transgress Shabbos?

Answer: Because it is a mitzvah to sanctify the month on the basis of eyewitness testimony.