The Zohar says that when the prayer of an individual (who is praying without a quorum) ascends before Hashem, Hashem also looks at the sins of that man, whereas when a prayer of a quorum ascends before Hashem, He does not look at their sins. There are many reasons why the prayer with a quorum is so important before Hashem: 1) As one is able to say “Amen”, “Yehei Shemih Rabbah Mevarach”, Barechu and Kedushah which are very valuable. 2) Because there is no comparison between a small number of people who perform a good deed and a large number of people who perform the same deed as when a large number of people perform it together it has much greater value. 3) As if an individual prays by himself without concentrating, or if he is a sinner etc., his prayer is not accepted. However, if he joins together with a quorum, it is accepted.
In our sins, there are many people who do not pray with a quorum without a good reason, and in the end they never pray with a quorum and think that it is completely permitted, and they go from bad to worse and end up praying a short, amputated, and snatched prayer, and in the end stop praying altogether.
