During our years in a former church my wife and I heard repeated admonitions from the leadership to greet visitors. Then a couple years ago we found ourselves looking for a new church community. Now we were the newcomers visiting various churches. In some of the communities I noticed an obvious personal connection between congregants that was not readily visible as a visitor in others.
The common thread was that the communities with this apparent “connectedness” had a single service and were smaller congregations . I can’t claim to be able to tease these observations apart. The impact of multiple services could simply be a matter of a meeting location that doesn’t work particularly well, such as with crowd bottlenecks in congested building entrances. But group size, on the other hand, seems to have some inherent dynamics beyond the physical constraints of a meeting place.
I’ve spent most of my working career inside of large organizations and something fundamentally different is going on among people in small social groups vs large ones. In large groups the organizational structure, whatever that happens to be, seems to consistently take on a life of its own and define the function of the group, rather than any shared sense of mission or purpose.
There is a good chance this is a byproduct our cognitive makeup. In the early 1990s British anthropologist Robin Dunbar observed a correlation between the average size of primate social groups and neocortex size . Dunbar extrapolated from that to calculate the number of stable social relationships that humans could comfortably have as somewhere between 150 and 200. He also made the following observation about human use of language, that it,
“…has two unusual properties that make it possible to form groups that are substantially larger than the 150-200 predicted by neocortex size: it allows us (1) to categorise individuals into types and (2) to instruct other individuals as to how they should behave towards specific types of individuals within society.”
In short, it allows us to organize, which suggests a fundamental insight about why organizational structures dominate how people interact when group size grows. Below the limit interaction is about social connection. Above the limit interaction is driven by categorization and instruction.
Since Dunbar first published there appears to be have been a fair bit of debate as to where this boundary actually is, as well as contrary voices pointing out that personal networks in the modern world can be far larger . I am not qualified to wander into the weeds here. All I am suggesting is that the boundary is real and has practical effects on the way social groups and organizing institutions work. And a good bit of political and economic theory seems to be blissfully unaware of it .
Why this matters to churches is that in the midst of theology and spiritual experience we seem to forget the limitations that characterize our physical existence. These just might include aspects of how our brains are wired. We are called into allegiance to the Body of Christ as part and parcel of our allegiance to the risen Lord. But it is possible that we can unnecessarily complicate the outworking of that when the structures we create don’t account for our material boundaries.
This problem seems to me to reach back into the ancient world. Group size was necessarily small when Christianity was a disfavored and sometimes persecuted minority. Faith can certainly come through preaching but in a hostile environment it would spread primarily via personal contact along social networks, such as families, work, and in the marketplace. Communities would be small and in periods of calm they could aggregate at the level of individual churches. But with numerical growth comes categorization and direction. And in learning how to do this the church absorbed the centralized authority practices of the surrounding culture.
And then Constantine’s official recognition of Christianity removed the limits to group size. At large scales centralized authority became a dominant feature of how the Church presented itself. It became an earthly kingdom that looked a whole lot like emperor, monarch, and baron. It is debatable how much this mirrored the kingdom Jesus describe to Pilate as “not of this world.”
We have the conceit in the modern world to believe we have put all this aside. But we also tend to uncritically absorb the authority and organizational structures from our own culture. And as our churches grow those structures come to dominate how they present to the world. Some of them have come to look a whole lot like corporations.
I am not trying to suggest that churches can’t ever be large, or that everything is inherently sweetness and light in small congregations. There are probably constructive ways that groups can grow in size and still foster stable community. There is nothing in Dunbar’s research to suggest that this is not possible.
But is is likely to require conscious thinking about limits as a church grows. Otherwise community is likely to be snuffed out by organization.
 By smaller I mean relative to what we were accustomed. We participated in the same community for nearly three decades. At the beginning attendance was a bit north of 300. At one point attendance peaked at roughly 1000. Relative to some mega-churches even this might be considered small.
 R.I.M. Dunbar, Neocortex Size as a Constraint on Group Size in Primates
Journal of Human Evolution 22(6):469-493. June 1992
 R.I.M. Dunbar. Coevolution of neocortical size, group size and language in humans.
Behavioral and Brain Sciences Volume 16, Issue 4 December 1993, pp. 681-694
 For an example see Barry Wellman, Is Dunbar’s number up?
British Journal of Psychology (2012), 103, 174–176
 This is probably why some of our grand ideas do not scale well. Consider, for instance, “from each according to his ability, to each according to his needs.” That probably only can work when the “eachs” all know each other. Or have reliable knowledge of reputation, and can readily identify freeloaders, liars and the power-hungry. The moment organization is applied to scale up the idea it becomes all about the apparatus required to collect from those with ability and distribute to those with need. A weak apparatus will collapse under the weight of the freeloaders. A strong apparatus will be dominated by the likes of Stalin and Mao.