Schaff, Philip. History of the Christian Church (The Complete Eight Volumes in One). Amazon Kindle Edition, 2014.
Volume 2, Ante-Nicene Christianity A.D. 100-325, “Chapter 1. Spread of Christianity.”
Schaff notes that there are not particular statistics in ancient literature, but he does list a number of sources, both in the ecclesiastical and secular literature, pertaining to the spread of Christianity. He follows this with additional works commenting on the early time of growth.
§4. Hindrances and Helps.
Christianity prior to Constantine was not recognized, then was considered a religion which could be punished. The Jewish origins and the outsider status of many followers of Christ created a highly negative attitude toward Christianity (Schaff 2014, Loc. 12278). However, Schaff notes that Christianity flourished even as people gave their lives for the Christian faith. Early Christians considered martyrdom as a “proof of the truth and holiness of the Christian religion” (Schaff 2014, Loc. 12290).
§5. Causes of the Success of Christianity.
“The chief positive cause of the rapid spread and ultimate triumph of Christianity is to be found in its own absolute intrinsic worth, as the universal religion of salvation, and in the perfect teaching and example of its divine-human Founder, who proves himself to every believing heart a Saviour from sin and a giver of eternal life” (Schaff 2014, Loc. 12310). Schaff sees Christianity as self-validating and applicable to all types of people everywhere. When compared to the relatively hopeless situation of Roman paganism of the day, it seems natural that people would flock to Christianity (Schaff 2014, Loc. 12313). Schaff notes that Gibbon, Lecky, and others have seen in Christianity a powerfulsocial force (Schaff 2014, Loc. 12340).