B'RAV AM HADRAS MELECH [b'Rav Am Hadras Melech]
(Mishnah): The Yisrael would slaughter (his Pesach), a Kohen did Kabalah, and Kohanim passed the blood one to another until the Mizbeach...
We involve many Kohanim due to "b'Rav Am Hadras Melech."
Berachos 8a (Rav Chisda): "Ohev Hash-m Sha'arei Tziyon mi'Kol Mishkenos Yakov" - Hash-m loves places where learning leads to definitive Halachah, more than all the Batei Kenesiyos and Batei Medrash.
Even though there were 13 Batei Kenesiyos in Tzipori. R. Ami and R. Asi would pray only where they learned.
Megilah 3a (R. Yosi bar Chanina): "Mishpachah u' Mishpachah" teaches that Kohanim and Leviyim abandon Avodah to go to hear the Megilah:
In Rebbi's house they abandoned learning Torah to hear the Megilah. Since we abandon Avodah to hear the Megilah. all the more so we abandon Torah to hear the Megilah!
5a (Rav): When the Megilah is read in the proper time, an individual may read it. It may be read early only in a Minyan.
Rambam (Hilchos Tefilah 8:3): A Beis Medrash is greater than a Beis ha'Keneses. Great Chachamim, even though they had many Batei Kenesiyos in their city, would pray only where they learned Torah, provided that there was Tefilah b'Tzibur there.
R. Yonah (Berachos 4a DH Ela): Tosfos says that it is better to pray in a Beis Medrash even without 10, than in a Beis ha'Keneses with the Tzibur. The Rambam says that the Beis Medrash is better only if there are 10 there. If so, what is the Chidush that the Beis Medrash is better? One might have thought that the Beis ha'Keneses is better because there are more people there, and b'Rav Am Hadras Melech. Even the Rambam requires 10 only for one who normally leaves his house to learn elsewhere. Since he is Batel from Torah to go to learn, he should pray with 10 or go to the Beis ha'Keneses.
Kesef Mishneh: I say that the Chidush is that it is better to pray in a Beis Medrash with 10 than in a Beis ha'Keneses with 10.
Kaf ha'Chayim (90:113): According to R. Yonah, even if there are more in the Beis ha'Keneses, the Beis Medrash is better. The Kesef Mishneh holds that they are the same. If there are the same number in each, the Beis Medrash is better. Alternatively, they discuss different laws. For one who learns in the Beis Medrash, it is better than the Beis ha'Keneses even if there are more in the Beis ha'Keneses. If he does not learn there, they are the same. If there are the same number in each, the Beis Medrash is better.
Rosh (Mo'ed Katan 3:85): Rabbeinu Meir ruled that Avelus (mourning) applies on Purim in private, like on Shabbos. After the Avel prays in his house, he goes to the Beis ha'Keneses for Kri'as ha'Megilah. Kri'as ha'Megilah overrides even Avodas ha'Korbanos, which overrides Shabbos. All the more so it overrides Avelus mid'Rabanan!
Beis Yosef (YD 401 DH u'Mah she'Chosav b'Shem): Why must we permit the Avel to go to the Beis ha'Keneses? They could read the Megilah in his house! We must say that there is greater Pirsum ha'Nes (publicity of the miracle) in the Beis ha'Keneses, due to b'Rav Am Hadras Melech.
Ran (Megilah 3a DH Amar): Even Rav agrees that the ideal Mitzvah is to hear the Megilah with the Tzibur, for Pirsum ha'Nes. Even if there are 100 in the Beis Medrash, it is better in the Beis ha'Keneses due to b'Rav Am Hadras Melech. However, Rav holds that one need not gather 10 to read it.
Shulchan Aruch (OC 8:5): If two or three put on Talesim at once, all bless. If they want, one blesses and the others answer Amen.
Sha'arei Teshuvah (7): Tevu'os Shor (19:7) says in the name of the Mabit that all may bless because they are not ready at the same time. Each would need to hold the Talis and wait. Likewise, regarding Tefilin they would need to wait with their arms exposed. The Mechaber holds like he wrote at the end of Siman 6 (regarding Birkos ha'Shachar) that everyone may bless for himself, just if they want one blesses for everyone.
Mishnah Berurah (8:13): The Shulchan Aruch connotes that it is better that everyone bless for himself. The truth is, it is best that one bless to exempt everyone, due to b'Rav Am Hadras Melech, like we say in 298:14. However, this is not the custom. Perhaps it is because not everyone is skilled to intend to be Yotzei and to be Motzi.
Shulchan Aruch (OC 90:18): A fixed Beis Medrash has more Kedushah than a Beis ha'Keneses. It is a greater Mitzvah to pray in a Beis Medrash than in a Beis ha'Keneses, as long as he prays with 10.
Magen Avraham (32): Even if there are more people in the Beis ha'Keneses, it is better to pray in his Beis Medrash to avoid Bitul Torah. We find that Rebbi used to pray only once a month! However, in Siman 298:14 (regarding blessing on fire in Havdalah) we say that we are Batel from learning for "b'Rav Am Hadras Melech"! We must say that there, it is only for a short time, so Chachamim were not concerned.
Mishnah Berurah (28): Acharonim say that if there is clamor in the Beis ha'Keneses with many people and one does not hear the Tefilah or Kri'as ha'Torah, it is better to pray in one's house with 10. If on Shabbos and Yom Tov one prays early with 10, because the Tzibur prays late, and there is time to go to pray Musaf in the Beis ha'Keneses with the large Tzibur, he should do so, due to b'Rav Am. This is if he normally prays in the Beis ha'Keneses. If not, he should pray the entire Tefilah in one place.
Shulchan Aruch (134:2): The one who lifts up the Torah shows it to people standing on the right and left, and in front and in back, for it is a Mitzvah for all men and women to see the writing, bow and say "v'Zos ha'Torah..."
Magen Avraham (2): The custom is that people run to the Beis ha'Keneses to see when they take out and return the Sefer Torah, even though for the rest of Tefilah they are outside, due to b'Rav Am.
Magen Avraham (147:11): One who sees a Mitzvah may leave to see another Mitzvah, even though it is a Mitzvah to see a (i.e. the first) Mitzvah due to b'Rav Am Hadras Melech.
Mishnah Berurah (229:8): It is good to say Birkas ha'Chamah amidst many people, due to "b'Rav Am Hadras Melech."
Kitzur Shulchan Aruch (60:7): One should not delay to say it amidst many people for this, for Zerizin Makdimim overrides "b'Rav Am."
Shulchan Aruch (426:2): We say Kidush Levanah only on Motza'ei Shabbos when one is wearing nice clothing.
Rema: If Motza'ei Shabbos will be after the 10th of the month, we do not wait, lest there be three or four cloudy days and he wil lose the Mitzvah. We do not say Kidush Levanah before Tish'ah b'Av or Yom Kipur. We may be Mekadesh on Motza'ei Yom Kipur, but not after Tish'ah b'Av or other fasts.
Magen Avraham (6): Keneses ha'Gedolah says that the custom is to be Mekadesh after a fast. Therefore, if an individual fasts, he should be Mekadesh with the Tzibur, due to b'Rav Am Hadras Melech. We are Mevatel even Talmud Torah for b'Rav Am Hadras Melech.
Bi'ur Halachah (DH Ela): Letter of the law, one may be Mekadesh by himself. It is only l'Chatchilah to do so amidst 10, for b'Rav Am Hadras Melech. If one knows that he will be able to be Mekadesh later with 10 people, he should wait only if it will be before the 10th of the month. The Chayei Adam says that three is also called b'Rav Am Hadras Melech, so one need not wait for 10, especially in winter when it is cloudy.
Kaf ha'Chayim (23): If the time for Kidush Levanah came, one should not delay in order to be Mekadesh amidst many people, for Zerizin Makdimim l'Mitzvos overrides "b'Rav Am" (Kitzur Shulchan Aruch 97:9).
Shulchan Aruch (689:5): Where there is not a Minyan, if only one knows how to read the Megilah, he exempts everyone. If all know, everyone reads for himself.
Magen Avraham (10): We must say that Kri'as ha'Megilah is like Tefilah, in which one needs a Minyan to be Motzi others. Some say that one may bless for everyone even without a Minyan, even if they know how to bless. If so, it is better to do so because of b'Rav Am.
Mishnah Berurah (15): Eliyahu Rabah, Mateh Yehudah and Derech ha'Chayim say like the Shulchan Aruch, that everyone reads for himself.