Church Growth

This is from Chapter 9 of the book Ancient Faith for the Church's Future which was written by Alan Kreider. The title of the chapter is "They Alone Know the Right Way to Live"--The Early Church and Evangelism.

"The ancient church was growing. From several thousands on Pentecost, the Christian movement spread rapidly, east to Syria and into the Persian Empire, south to Egypt and across North Africa, north and west to Asia Minor and to what we call Europe. As it spread geographically, it grew numerically. By the time of Constantine I's accession to the throne in the early fourth century, the Christian communities within the Roman Empire, scattered unevenly, had come to comprise approximately six million people--one tenth of the imperial populace. According to one scholar, this represents a growth, on average, of approximately 40 percent per decade. Christianity was an illegal cult, subject to imposing variety of disincentives, so its early growth is formidable and question posing. Why did the early church grow?"

More on this later....but they did not grow because they were "user friendly" or were even culture-relevant. Why did they grow so much?