Helmut Koester (of Harvard Divinity School) says this...
"Now we have increasingly in the Christian churches, in the time up to Constantine, the establishment of hospitals, of some kind of health service, we have a clear establishment of social service - everything from soup kitchens to money for the poor if they need it. We have the very important establishment of the institution of widows, because a widow in the Roman society who had lost her husband and did not have money of her own was at the very bottom of the social ladder. One of the first welfare institutions we find in the church was all the widows who were recognized as virgins of the church, considered particularly precious possessions of the church; they were paid by the church and therefore were rescued from utter poverty in most instances.
Christianity really established a realm of mutual social support for the members that joined the church. And I think that this was probably in the long run an enormously important factor for the success of the Christian mission. And it was for that very reason that Constantine saw that the only thing that would rescue the empire is to take over the institutions that the Christians had already built up, [including], by that time, institutions of education in reading and writing, because Christians wanted to have their members knowledgeable and capable of reading the Bible.... We find that in administration of the last pagan emperors, before Constantine, at the very end of the third century, a large number of the people in the imperial administration are Christians, because they could read and write. Which constituted a big problem with the persecution of the Christians because they were thrown out of their office first when the persecution began, and suddenly the government didn't work anymore.
One should not see the success of Christianity simply on the level of a great religious message; one has to see it also in the consistent and very well thought out establishment of institutions to serve the needs of the community."