After the testimony of faith, the prayer is the most important of all commandments in Islam. One of the most important aspects of the prayer for men is to pray the obligatory prayers in congregation (known in Arabic as jamā'ah). This should normally take place in the local mosque; however, even when there is no mosque nearby, the obligatory prayers must still be offered in congregation. As for women, they are not required to pray in congregation, but they may do so if they wish, and if there are appropriate facilities available.
The seriousness of praying in congregation is shown in the following verse of the Qur'an:
"When you (O Messenger Muhammad) are among them, and lead them in As‑Salaah (the prayer), let one party of them stand up [in Salaah (prayer)] with you taking their arms with them; when they finish their prostrations, let them take their positions in the rear and let the other party come up which have not yet prayed, and let them pray with you" [The Qur'an: an-Nisā' 4:102]
The following points are made on the basis of this verse:
Allah commands the believers to pray in congregation, then He repeats this command a second time with regard to the second party or group, as He says, “and let the other party come up which have not yet prayed, and let them pray with you”. This indicates that prayer in congregation is an obligation for all individuals, because Allah did not absolve the second group of this obligation as a result of the first group having prayed in congregation. If prayer in congregation was only something recommended, it would be more appropriate for people to be excused from it at times of fear [the situation referred to in this verse], and if it were a communal obligation, it would be discharged by the actions of the first group. So this verse shows that it is an individual obligation upon every male Muslim.
The second proof to show how serious praying in congregation is the following narration:
Abū Hurayrah (may Allah be pleased with him) narrated that the Messenger of Allah (may the peace and blessings of Allah be upon him) said:
"By the One in Whose hand is my soul, I had thought of ordering that wood be gathered, then I would command the call to prayer to be given, and I would appoint a man to lead the people in prayer, then I would go to men [who do not attend the congregational prayer] and burn their houses down around them. By the One in Whose hand is my soul, if anyone of you had known that he would receive a bone covered with meat or two (small) pieces of meat from a sheep's foot, he would attend the 'Ishā' prayer.” [al-Bukhārī: 7224; Muslim: 651]
There are many benefits of praying in congregation, one of the greatest being that the reward of your prayer is multiplied many times over, as mentioned in the following narration:
"Prayer in congregation is twenty-five levels better than a prayer offered on one's own." [an-Nasā'ī: 839]
Narrated `Abdullah bin `Umar: Allah's Messenger (May the Peace and Blessings of Allah be upon him) said:
"The prayer in congregation is twenty seven times superior to the prayer offered by person alone." [al-Bukhārī: 646]
Praying in congregation also gives you protection from the devil, as is mentioned in the following narration:
Abū ad-Dardā' narrated that he heard the Messenger of Allah (may the peace and blessings of Allah be upon him) say:
"If there are three men in a village or in the desert among whom prayer is not offered (in congregation), the devil has got the mastery over them. So observe (prayer) in congregation, for the wolf eats only the straggling animal." [Abū Dāwood: 547]