"The basic point which emerges is that the earliest house churches, in most cases, must have been fairly small, a dozen or twenty people in all. And even when ‘the whole church’ in a city or section of a city could meet as church in one place, we may very well be talking of only forty or fifty people, and not necessarily gathered in a single room. The dynamics of church life, of the shared life of believers in most cities, must have been dependent on and to some extent determined by the physical space in which they were able to function as church. We, of course, are accustomed to visualizing huge church buildings and congregations which can be numbered in the hundreds or even thousands. So it is important for us to remember that the typical church of the first century or more of Christian history was the gathering of small cell comprising twenty or so, and less regularly up to about fifty. This is important, since we are now well aware that the social dynamics of small groups is very different from that of large groups. And the accompanying theology needs to take such factors more into account than is usually the case. In many cases our concern should be not that our churches are too small but that they are too large!"
James D. G. Dunn, Jesus, Paul, and the Gospels (Grand Rapids: Eerdmans, 2011), 171.