1) Tosfos in Nazir 2b writes that although the Ta'anis is ostensibly a positive act and is able to counter punishment threatened by the dream, nevertheless the neglect of Oneg Shabbos requires somewhat of a Kaparah. He compares this to Nezirus, which is a Mitzvah but still requires Kaparah since he deprived himself.

This may also be understood as follows. Although the situation that he was in (the dream or the necessity to become a Nazir) required the action, nevertheless, had he been totally righteous he would not have been subjected to the situation of having to fast on Shabbos.

2) As for Mordechai's fast and the Simcha of the building of the Beis Hamikdosh, we are enclosing notes from the Kollel on those subjects.

3) As for the alternatives you offered in point three, the Gemara in Shabbos 11a writes that a fast is the best thing for a dream and therefore the alternatives are only second best.

Dov Zupnik

Another way to understand the sin+Mitzvah combination is as follows. The person who made himself a Nazir or fasted for his dream on Shabbos did drastic Teshuvah. Had he had more Bitachon in Hash-m, he would have trusted that he can do a less drastic form of Teshuvah, and whatever he suffers at the hands of Hash-m as Yisurim she'Memarkin Avonosav he will accept with love.

-Mordecai Kornfeld

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From Insights to the Daf: Moed Katan 9:1

1) AGADAH: THE YEAR THE JEWISH PEOPLE DID NOT FAST ON YOM KIPUR

QUESTIONS: When the building of the Beis ha'Mikdash was completed in the times of Shlomo ha'Melech, the Jewish people experienced great joy and they celebrated for seven days prior to Sukos, as the verse relates (Melachim I 8:65). That year, says the Gemara, the Jewish people did not observe the fast of Yom Kipur, as they ate on that day as part of the celebration of the Chanukas ha'Mikdash.

The Gemara says that they derived their allowance to eat on Yom Kipur from the Torah's description of the Chanukas ha'Mishkan in the Midbar. When the Mishkan was dedicated, the Nesi'im brought Korbanos as part of the celebration, and they brought them even on Shabbos. The Jewish people learned from there that when the Mikdash is dedicated, the celebration overrides the obligation to fast on Yom Kipur. Hash-m was pleased with this ruling, and at the end of the celebrations, a Bas Kol issued forth saying that they were all destined to Chayei Olam ha'Ba.

The Gemara says, however, that before the Bas Kol issued forth, the Jewish people were worried that they had transgressed by eating on Yom Kipur and would be punished with destruction (Kares).

Why did they think that they were liable for punishment? Even if they made a mistake, at worst it was an inadvertent transgress, an act of Shogeg, for which there is no punishment of Kares. Besides, certainly the people were following the ruling of Beis Din in this matter, so how could they be held accountable! At worst, the people would be Chayav to bring a Par he'Elem Davar (the Korban which is brought when the entire nation acts upon an erroneous ruling of Beis Din which permits an act that is actually forbidden with a punishment of Kares). Why were they afraid that they would be punished with destruction?

Second, the Gemara implies that their Derashah was indeed correct, and Hash-m was pleased with the Simchah that they experienced on that Yom Kipur. Why, then, does the Gemara ask, "How do we know that Hash-m forgave them," and why does it refer to their eating on Yom Kipur as "the sin of Yom Kipur." If they based their actions on a proper Kal v'Chomer, why does the Gemara call it a "sin," and why did they need forgiveness? (CHIDUSHIM U'VIURIM)

ANSWER: It must be that at the Chanukas ha'Mikdash, the Beis Din did not actually issue a ruling permitting (or requiring) the people to eat on Yom Kipur. In fact, the Beis Din did not convene at all to discuss the question. Rather, the people themselves, and the members of the Beis Din together with them, were so excited and euphoric about the inauguration of the Beis ha'Mikdash, the dwelling place for the Shechinah in this world, that they spontaneously assumed that it was permitted to celebrate even on Yom Kipur, based on the Kal v'Chomer. They assumed that there was no need to convene Beis Din to issue a Heter. Their joy was so great and their longing to express it so intense, that by common consent they decided to express their joy through eating despite Yom Kipur. Even though they based this ruling on a Kal v'Chomer, and they did not intentionally transgress the laws of Yom Kipur, their mistake in the Derashah, they feared, would be counted against them as an intentional act of transgression, for "Shigegas Talmud Oleh Zadon" (Pirkei Avos 4:13) -- a mistake in learning is considered to be a knowledgeable transgression.

What was their mistake in their Kal v'Chomer? The Gemara explains that their Kal v'Chomer was derived from the Korbanos of the Nesi'im, from which they learned that it is permitted to override the laws of Shabbos, and Yom Kipur, for the sake of celebrating the Chanukas ha'Mikdash. The Gemara asks, though, that we can only learn from there that Korbanos of the Chanukah override Shabbos, not that physical expressions of joy, such as eating, override the obligation to fast on Yom Kipur. How did they know that they could also permit eating and drinking on Yom Kipur? The Gemara answers that "there is no Simchah without eating and drinking."

The TOSFOS HA'ROSH asks, that is true if they had a source for a Mitzvah d'Oraisa to express Simchah upon the completion of the Mikdash. However, all that can be learned from the Korbanos of the Nesi'im is that Korbanos must be brought when the Mikdash is built! Where did they see an obligation to express joy -- through eating and drinking -- as well as bringing Korbanos?

The Tosfos ha'Rosh answers that they considered the obligation to rejoice to be an obvious corollary of bringing Korbanos, since whenever Korbanos are offered, there is Simchah, as the verse says, "You shall offer sacrifices and eat them and rejoice before Hash-m." (Devarim 27:7)

This answer needs further elucidation. All that can be seen from the verse in Devarim is that one must rejoice in the offering of the Korban , not in the building of the Mikdash. There is no source to show that the joy of offering a Korban overrides Shabbos and Yom Kipur! We only see that the celebration of building the Mikdash has such a status. If so, why did the Jewish People think that their joy should override Yom Kipur?

It must be that their logic was as follows. Why, they asked, did Hash-m tell the Nesi'im to offer their Korbanos on Shabbos? It must be because one cannot celebrate properly (in the times of the Mikdash) without eating the meat of Korbanos (Pesachim 109a, based on the above-mentioned verse in Devarim). Hash-m allowed the Korban to be brought on Shabbos in order that there should be Simchah that day, through the offering and eating of the Korban.

If so, this was their mistake. They were attempting to read their own reasons into the commandments of the Torah (Doresh Ta'ama d'Kra) and derive Halachos in that manner, using a method that is not one of the accepted 13 principles of Halachic exposition. For that reason, their act was called a sin, and required atonement. Nevertheless, a Bas Kol issued forth and informed them that since what they did was done purely for the sake of honoring Hash-m, they would not be punished. They were even rewarded for their pure intentions. (M. Kornfeld. See also Sanhedrin 21b, "Why were the reasons for the Mitzvos not revealed? Because in the two instances in which they were revealed, the greatest person in the world ( King Shlomo ) erred... "I will marry and I will not be affected...," Y. Shaw.)

Regarding the question of how Mordechai and Esther could make a decree to go against an explicit Mitzvah in the Torah, there is a lengthy discussion in the Gemara in Yevamos (89b-90b) regarding how Beis Din can make a decree to uproot a Torah law. The Gemara concludes with the famous principle that "Shev v'Al Ta'aseh Shani" -- the Rabbis have the authority to make a decree where they see fit even though it will cause a Mitzvah in the Torah not to be done. (The classic example of this is the decree not to blow the Shofar on Rosh Hashanah when Rosh Hashanah occurs on Shabbos, which the Rabanan instituted out of concern that blowing the Shofar on Shabbos would lead to carrying it through a public domain, the Melachah of Hotza'ah.)

However, this might not apply in the case of Mordechai's decree to fast on the first day of Pesach, because perhaps the allowance to annul a Mitzvah in the Torah through passive inaction is a right reserved only for Beis Din, when Beis Din convenes and enacts a decree in the formal, judicial manner, but individual leaders do not have this right. In the case of Purim, it can be argued that it was Mordechai alone, as the leader of the Jewish people, who decreed the fast (at Esther's bequest), and it apparently was not done through a formal convening of Beis Din. (This is not a question, though, according to the view in the Gemara in Megilah (14a) that Esther was a Nevi'ah, a prophetess, and Mordechai was a Navi, for the Gemara in Yevamos there cites verses in the Torah which prove that it is permitted for a Navi to temporarily annul a Mitzvah in the Torah when the need arises, as we see also in the case of Eliyahu ha'Navi.)

The answer to the question is found in the Midrash Rabah (Parshah 8) on Megilas Esther. When Esther told Mordechai to issue the decree to fast for three days, Mordechai questioned that the fast would include the first day of Pesach. Esther responded that the whole purpose of Pesach is for the Jews to observe the Mitzvos, but if there are no Jews, what point is there in having Pesach? (This is similar to the dictum that explains why it is permitted to desecrate Shabbos in order to save a life: "Desecrate one Shabbos in order to observe many more" (Yoma 85b).) Thus, fasting on Pesach was an act of Piku'ach Nefesh (fasting and praying in order to save lives) due to the decree of annihilation that had been issued against the Jewish people. Once we understand the context in which the decree to fast was made (that of mortal danger), and we understand that fasting and prayer are indeed effective instruments for winning Divine favor and annulling heavenly decrees, the question is how could they have had a Havah Amina not to uproot a Mitzvah in the Torah; when the entire Jewish people is in mortal danger, it is certainly permitted to be Mevatel a Mitzvah!

(The Sifsei Chachamim to Megilah 15a says that the three-day fast had the status of a "Ta'anis Chalom," which may be made even on Shabbos and even on Yom Tov in order to annul a heavenly decree. So, too, the fast at the time of Purim was made to annul a heavenly decree that was issued against all of Israel.)

(However, there seems to be evidence that in truth, they did not fast on the first day of Pesach at all. They only thought that they did. In reality, though, Beis Din had been Me'aber the Chodesh (Adar) in Eretz Yisrael, and news of the extra day of Adar had not yet reached Persia. Thus, the third day of the fast was actually the day before Pesach!)

See also three or four more answers given by the Aruch La'ner and the Ya'aros Devash. (For example, they relate to the Machlokes between the Medrash and the Targum concerning whether the three-day fast was for three days and three nights, or just three days (and "the nights" mentioned refers to Tefilah, and not to fasting. They also discuss the idea that the shiur of Inuy is a Koseves (dried fig), while the shiur of Achilas Matzah is a small shiur, that of a k'Zayis.)