In the Marquette Lecture volume, I focus on the question in the title. I emphasize the social and political costs of being a Christian in the earliest centuries, and contend that many attempts to answer the question are banal. I don't attempt a full answer myself, but urge that scholars should take the question more seriously.

"Religions" of the Roman world varied. Most of it was ritual practices. There were periodic occasions when cities honored their guardian deities with sacrifices and ceremonies, to ensure that they stayed happy and kept the city safe.

[Christians] practiced moderation and chastity in marriage, for example, and Galen was puzzled at how they were able to do so. His comments are a kind of back-handed compliment, I suppose.

Some modern scholars contend that in terms of what "religion" was in that [Roman-era setting], you can't even call Christianity a religion.

Justin Martyr says that he was impressed in his study of the Old Testament, at the seriousness and contents of these writings, and became convinced that Jesus fulfilled these texts.

Justin's testimony about becoming a Christian is that he had been searching various philosophical traditions of the time, and then accidentally encountered a man who posed questions that pointed Justin [Martyr ] in a new direction.

I think that Rodney Stark studies of new religious movements in the modern world give us some insights into the kinds of questions that we can ask about early Christianity.