Galen's observations reflect one of the distinctive features of early Christianity. Roman-era religion was mainly about ritual actions vis-à-vis the gods, and there was little to do with ordering behavior otherwise.

"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.

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.

In its Roman-era setting, for example, Christianity was so different that critics of the time referred to it as a "superstition" (meaning a bogus or dangerous religion).

I think Rodney Stark makes a substantial contribution to the study of early Christianity in posing the kinds of questions that he pursues (which reflect his social-science background).

Studies of the people named and described in earliest Christian texts show that, right from the earliest years, they included craftsmen, merchants, and owners of businesses. Of course, there were also slaves and poor among believers. By at least the second century, there were also believers from upper levels of Roman society.

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.