From the following blog: "Ten Reasons: the observations of a seditious catechist"
In a fascinating, recently made-available interview with Mike Aquilina, historian and sociologist Rodney Stark shows what really made the early Church grow and thrive:
You also argue for steady growth by individual conversions rather than by mass conversions. Why?
RS: We don't have a single documented case of mass conversion. Yes, there's the passage in the Book of Acts, and I'm not one of these people who say, "Don't trust the Bible." But you've got to understand what people meant by numbers in those times. Numbers were rhetorical exercises. You'd say a million when you really meant a hundred. What you're really saying is "lots." In Acts, I think the numbers are meant to say, "Look, wonderful things are happening." If the historical demographers are right, Jerusalem had about 25,000 people in it at the time. So if you start talking about eight or ten thousand converts, that's a little bit out of scale.
What about forced conversions?
RS: There weren't any in the time I'm talking about. Constantine didn't cause the triumph of Christianity. He rode off it. In fact, I'll go so far as to say he had many harmful effects. I don't believe establishment is good for churches. It gets them involved in the worldly realm in ways that are unsuitable and corrupting. By the end of Constantine's reign, we see people competing madly to become bishops because of the money. After that, Christianity was no longer a person-to-person movement.
Emperor Constantine did not so much ensure Christianity's success as acknowledge it. Constantine's edict of toleration in 313 was overdue recognition that the Church had already won the empire.
You look at the spread of Christianity beyond the empire, and you see that it was almost entirely by treaty and by baptizing kings. I think one reason medieval church attendance was so bad in Scandinavia and Germany was that these people weren't really Christians. If it hadn't been for the establishment of the Church, they might have been. Their lands would have become Christian because many people would have gone door-to-door to make Christians out of them -- and then baptized the king. It was bad for the Church. I think the current pope would agree with me; I think most medieval popes would have me burned for saying this.
American Catholics can understand it, though. They know how good it was for the Church to have to fight for its life in the United States. The old Protestant story was that the priest met the boat, and you had another boatload of Catholics. But that's not true; those people weren't used to going to church or contributing money. They had to be turned into Catholics. It was a remarkable feat. Posed with a challenge, the Church rose to it very well, and the American Church became a very strong Church, compared to the Latin American Church.
The received tradition is that many Christians were martyred. Yet you say that blood witnesses were few.
RS: There's a consensus among historians that the numbers weren't large at all, and that we may know the name of just about every single martyr. The Romans decided to attack the movement from the top. This would have worked with other religions because there was no bottom to paganism. Paganism was really temples on a shopping mall, and people were very casual about which ones they patronized. If the Romans knocked off the chief priest and took away government subsidy, a pagan temple would fold up.
So the empire went after Christianity the same way, thinking, "If we butcher the bishops, things will take care of themselves." Of course, it didn't work because there were 92 guys waiting in line to be bishop. That's what you get with a mass movement.
What was true then -- and true centuries later on this continent -- is still true now: Christianity is fundamentally a person-to-person movement. Studies of converts bear this out as well. While they often cite core doctrines like the Eucharist, papal authority, or the defense of human life, converts just as often tell you it was because of a person that they became Catholic. One of the tragedies of Vatican II's flawed implementation is that it clericalized the laity, convincing them that their vocation was in and around the sanctuary, where they work amongst themselves and compete with the clergy, instead of out in the world, where they can evangelize and build a civilization of love. You can read Mike Aquilina's 36-page history of the early Church for the Knights of Columbus here.