Calvin: "I call it a private mass whenever there is no communion among believers in the Lord's Supper, even if a large crowd of people are otherwise present" (Institutes 4.8.7).
Calvin is talking about a priest doing the Eucharist with the gathered people not communing. It's "private" even if there's a lot of people in the room while it's being performed by the priest because no one but the priest is partaking of the bread and wine.
Of course, private masses are still performed for various reasons by Roman priests. But the Roman church has reintroduced communion in both kinds as well as regular congregational participation at the weekly Supper. The Reformation was pretty successful in dealing with the late medieval problem of the withdrawal of the laity from the Table.
But there's another problem with the way modern Christians celebrate the Lord's Supper that might be labeled as "private mass" or maybe just "private communion." The word "communion" refers not only to our communion with the resurrected Jesus through the bread and wine at the Supper. There's also a horizontal dimension to the Table that flows from union with Jesus. We are united with one another. We commune with Jesus and with one another. "Because there is one loaf, we who are many are one body, for we all partake of one loaf" (1 Cor. 10:17).
But how is our communion with one another expressed at the Table? In most churches hardly at all. I would suggest that there's another kind of "private mass" going on. Everyone in the congregation curls up in his own little personal world to take communion. We don't look at anyone else. We don't talk to the person sitting next to us. We just work up private devotional thoughts and eat and drink by our lonesome. To extend Calvin's quote:
"I call it a private mass whenever there is no communion between believers at the Lord's Table, even if a large crowd of people are otherwise present"
The problem with this is that meals, even ritual meals are not simply about personal, private nourishment. They are social events. Think of the family meal. Do the individual members of the family simply gobble up the food and slurp down their drinks without acknowledging others at the Table? Of course not. We would judge any family to quite dysfunctional if nobody said a word to anyone else at the dinner table. All meals are communal events. Take away the communal dimension of a meal and you are left with the private ingestion of nutrients.
So why don't Christian's acknowledge one another at the Lord's Table? Why don't we talk to one another? Why doesn't the Lord's Table have the same sort of communal conversation and joyous interaction as a healthy family meal? Why do Christians think that the Lord's Supper is the time for intense personal examination and private devotional thoughts? We have time for that sort of thing all week. What we don't experience at any time during a normal week is the presence of our brothers and sisters in Christ gathered as the body of Christ at the Communion Table.
The Reformation rightly corrected a certain kind of privatization of the Supper. But the way Communion is practiced in most churches today makes one wonder if we didn't just multiply private masses. It's not just the priest that communes alone; rather, now everyone at the Communion service thinks of the Table as his own private time. Think about it.