For your consideration, below is a quote from C.S. Lewis in regards to Christians gathering for common worship. In this quote you will find one reason that we are required by our Mother the Church to attend Mass on every Sunday and Holy Day of Obligation.

No Christian and, indeed, no historian could accept the epigram which defines religion as “what a man does with his solitude.” It was one of the Wesleys, I think, who said that the New Testament knows nothing of solitary religion. We are forbidden to neglect the assembling of ourselves together. Christianity is already institutional in the earliest of its documents. The Church is the Bride of Christ. We are members of one another.

More on this quote later because there is something else to take into consideration here. What happens when mankind starts to treat religion as something that is done in solitude?