The Christians were just as susceptible as the pagan population to the diseases. But they responded in profoundly different ways:
Here issues of doctrine must be addressed. For something distinctive did come into the world with the development of Judeo-Christian thought: the linking of a highly social ethical code with religion. There was nothing new in the idea that the supernatural makes behavioral demands upon humans--the gods have always wanted sacrifices and worship. Nor was there anything new in the notion that the supernatural will respond to offerings--that the gods can be induced to exchange services for sacrifices. What was new was the notion that more than self-interested exchange relations were possible between humans and the supernatural. The Christian teaching that God loves those who love him was alien to pagan beliefs. MacMullen has noted that from the pagan perspective "what mattered was ...the service that the deity could provide, since a god (as Aristotle had long taught) could feel no love in response to that offered." Equally alien to paganism was the notion that because God loves humanity, Christians cannot please God unless they love one another. Indeed, as God demonstrates his love through sacrifice, humans must demonstrate their love through sacrifice on behalf of one another. Moreover, such responsibilities were to be extended beyond the bonds of family and tribe... These were revolutionary ideas...This difference in doctrine was born out in practice during the epidemics. The pagans fled the cities and left the sick to take care of themselves. The Christians stayed and took care of the sick, all of the sick. Both Christian and pagan correspondence from the period bears this out.
What affect did this have on Christian conversion? Well, it is easy to imagine that those who were cared for and lived would have been more open to hearing the Christian message. But the interesting scientific corollary is that more sick people lived because of this care. The Christians, of course, could do nothing about the disease itself. But:
McNeill pointed out: "When all normal services break down, quite elementary nursing will greatly reduce mortality. Simple provision of food and water, for instance, will allow persons who are temporarily too weak to cope for themselves to recover instead of perishing miserably."So the "unusual" practice of intentionally caring for the sick practiced by the Christians actually meant that more people lived through the epidemics. It would have looked and felt like a miracle. Whose God is real? In addition, and this hearkens to an earlier chapter in the book, since conversion almost always happens through bonds of friendship and family, and people are less likely to convert to a religion if they already have strong social and religious ties, the epidemics severed the social and religious ties of many pagans and opened them emotionally to be willing and ready to respond to the novel religious claim of Christianity.
...Modern medical experts believe that conscientious nursing without any medications could cut the mortality rate by two-thirds or even more...