As discussed previously, there are several benefits to congregational prayers. As well as the spiritual uplifting and personal satisfaction, authentic traditions as quoted in Ayatollah Sayyid Ali Sistani's Islamic Laws state that congregational prayers are 25 times better than praying alone. Such is the reward that it is highly recommended for a person who has already offered his prayers alone to repeat his prayers in congregation.
A basic introduction to congregational prayers is provided in every Religious Authority's (Marja Taqleed) code of practice. Ayatollah Sistani's book is available on his website www.sistani.org, and Ayatollah Sayyid Ali Khamenei's is available on www.leader.ir. The information provided is so detailed that for every reason we are unsure, our questions are answered and our doubts are eliminated.
What we must remember is that there are certain rules and protocols we must follow and be aware of during congregational prayers. The first aspect is the Imam, the one leading the prayers. According to almost all Religious Authorities, the Imam leading the congregational prayers should be an adult (having reached puberty or 15 years of age for males or 9 years of age for females), sane, Twelver Shia Muslim, just, of legitimate birth, and able to perform the prayers correctly. If the followers of the Imam are male, then the Imam must also be male. (The concept of who qualifies as "just" is also discussed in detail in the manuals of jurisprudence. Suffice to say, it is one who avoids all big and small sins and is generally considered a good person in his community.)
The next step to congregational prayers is to understand what our duty is as the follower of the Imam. If the Imam leading is a female, and you too are female, then it is an obligatory precaution for you to stand in line with the Imam. However, if the Imam is a male, and you are a male, then you will stand a little behind the Imam. If there are women in that congregation, they will stand a little further behind the men. Our questions of what we should recite and shouldn’t recite in congregational prayers, our intention, and what mistakes are possible to occur are all answered in our Religious Authority's code of practice.
It is highly recommended for the Imam to stand in the middle, while the first row behind him is occupied by those who are learned and pious. How does one know whether to stand in the first row or further behind? You ask yourself: where do you consider yourself to be on the scale before Allah? Are you up to par with your deeds and confident to stand firmly as one who strives in His way alone? If the Imam were to unintentionally invalidate his prayer, the person standing right behind him might have to step up and become the new Imam. For every step of congregational prayer, there is a process of understanding, a process requiring us to use our reasoning and logic, as ordained by Allah.
It is also recommended for the rows of congregational prayer to be arranged in such a manner that there is no gap between the people standing in one row, with everyone standing shoulder to shoulder. Such is the consideration of giving everyone a chance in congregational prayers that it is said in the book of Islamic laws that if an Imam is in Ruku (bowing) and realizes that somebody has entered the mosque and would like to join the prayer, the Imam should prolong his Ruku, giving the person a chance to join.
It is also important to keep in mind the things which are Makrooh, or discouraged, in congregational prayers. For example, if there is a vacant space in the rows of congregation, it is recommended for a person not to stand alone.
Reading these laws of congregational prayers, we come to understand that Allah's Mercy and Wisdom is beyond our comprehension, and the opportunities He has given us to excel in our performance and deeds in front of Him are also beyond our imagination. We can only thank Allah, by maximizing the use of these opportunities He has given us, while asking for nothing in return.