Mishneh Torah (Rambam) משנה תורה

Communal prayer is always heard. Even when there are transgressors among [the congregation], the Holy One, blessed be He, does not reject the prayers of the many. Therefore, a person should include himself in the community and should not pray alone whenever he is able to pray with the community. One should always spend the early morning and evening [hours] in the synagogue, for prayer will not be heard at all times except [when recited] in the synagogue. Anyone who has a synagogue in his city and does not pray [together] with the congregation in it is called a bad neighbor.

It is a mitzvah to run to the synagogue as [Hoshea 6:3] states: "Let us know. Let us run to know God." A person should not take long steps when he leaves the synagogue. Instead, he should proceed [slowly,] step by step. When one enters a synagogue, he should go in the distance of two doorways and then pray, [in order] to fulfill [the instructions of Proverbs 8:34] which states: "to guard the posts of My doors."

A study hall is greater than a synagogue. Even though [some of the] great Sages [lived in] cities where many synagogues were located, they would pray only in the place where they studied Torah. The above applies, [however, only] when one can participate in communal prayer there.

What is implied by [the term,] communal prayer? One [person] prays aloud and all [the others] listen. This should not be done with fewer than ten adult free males. The leader of the congregation is [counted as] one of them. Even if some of them have already prayed and fulfilled their obligation, they can complete the [quorum of] ten provided the majority of the ten have not prayed. Similarly, we should not recite Kedushah, read the Torah with its blessings before and after it, or read the haftorah from the Prophets except in [a quorum of] ten.

Similarly, one [person] should not recite the blessings associated with the Shema while the others listen and answer "Amen" except [in the presence of a quorum of] ten. This is called poreis al Shema. One only recites Kaddish with ten. The priests do not bless the people except [in the presence of a quorum of] ten. The priests [themselves] may be considered part of the quorum. [Ten are required] because every [group of] ten Jews is called a congregation as [implied by Numbers 14:27]: "How long [must I suffer] this evil congregation." They were ten, for Joshua and Calev were not included [among them].

Any holy matter may only [be performed] in a congregation of Jews, as [Leviticus 22:32] states: "And I shall be sanctified among the children of Israel". Regarding all these matters, if they were begun with ten [people] and some leave - even though they are not permitted to - the remainder should conclude [the holy matter].

All [ten members of a congregation] and the leader of the congregation must be in one place. [The following rules apply when] a small courtyard opens up in its entirety into a large courtyard: If there are nine [people] in the large one and one in the small one, they may be considered as a group [to form a quorum of ten]. If there are nine [people] in the small one and one in the large one, they are not considered as a group. If a congregation is in the large one, but the leader of the congregation is in the small one, they fulfill their obligation. If the congregation is in the small one, but the leader of the congregation is in the large one, they do not fulfill their obligation since he is separate from them and not with them in one place. [The motivating principle is] that the walls on each side of the large courtyard separate it from the small one. [However], the smaller one is not separated from the large one, but rather, is considered as its corner.

Similarly, if there were feces in the larger [courtyard], it is forbidden to pray or recite the Shema [even] in the smaller one. If there were feces in the smaller one, it is permissible to pray and recite the Shema in the larger one provided there is not a foul odor since [the larger courtyard] is set apart from [the feces].

The leader of the congregation can fulfill the obligation [of prayer] on behalf of the congregation. What is implied? When he prays and they listen and respond "Amen" after each and every blessing, it is considered as if they prayed [themselves]. To whom does this apply? To one who does not know how to pray. However, one who does know how to pray, only fulfills his obligation by praying himself.

When does the above apply? Throughout the entire year with the exception of Rosh HaShanah, and Yom Kippur of the Jubilee year. On these two days, the leader of the congregation can fulfill the obligation [of prayer] on behalf of those who know [how to pray] just as he can fulfill the obligation [of prayer] on behalf of those who do not know [how to pray] because [the Shemoneh Esreh recited on these days contains] long blessings and most people do not know them [to the extent] that they can have the same intention as the leader of the congregation. Therefore, on these two days, even a person who knows [how to pray] is granted permission to rely on the prayers of the leader of the congregation to fulfill his obligation [of prayer] if he so desires.

Only a person of great stature within the community in both wisdom and deed should be appointed as the leader of the congregation. If he is an older man, it is very praiseworthy. An effort should be made to appoint as the leader of the congregation, someone who has a pleasant voice and is familiar with reading [Biblical verses]. A person who does not have a full beard should not be appointed as the leader of the congregation even if he be a wise man of great stature, as a gesture of respect to the congregation. However, he may recite the Shema publicly after he has reached the age of thirteen and manifested signs of physical maturity.

Similarly, the inarticulate who pronounce an alef as an ayin or an ayin as an alef or one who cannot articulate the letters in the proper manner should not be appointed as the leader of a congregation. A teacher may appoint one of his students to lead the prayers in his presence. A blind person may recite the Shema publicly and serve as the leader of a congregation. A person whose shoulders are uncovered - though he may recite the Shema publicly - may not serve as the leader of the congregation until he is covered by a cloak.