Rodney Stark notes the importance of personal networks in the early growth of Christianity.
Two things are important to understand about how this kind of sense of community facilitated the rapid growth of the church. And one is, of course, that it was very attractive to an outsider, seeing how their life could be changed. But the other part of it is that conversion isn’t something that happens because people are walking … are looking across the street and seeing this group and saying, I’m going to go run join them, or they hear a revival preacher or whatever. People join through their friends, they join through networks. And as people spread the faith, it was going to their brothers and their sisters and their neighbours and their relatives and their employers and their employees, and that’s the way it spread. And so the sense of community was essential to the whole growth. It was, in a sense, a community that adopted Christianity in that sense.