The best guess seems to be that,
immediately before the emperors
Constantine and
Licinius issued the
Edict of Milan in 313 AD,
about 5 percent to 10 percent of the population of the Roman Empire
was Christian. Although these percentages may seen low, they
translate to millions of converts. Assuming a total population of
about 55 million in the Roman Empire at the time, the number of
Christians would have been somewhere between 2.75 million and 5.5
million.
And yet, as Ramsay MacMullen notes in
Christianizing
the Roman Empire A.D. 100-400, a profound mystery remains as to how
Christianity had acquired so many converts. “After New Testament times
and before Constantine,” there is almost no evidence of “open
advertising” of Christianity, and much evidence that Christians
were urged to lay low and to associate only with other Christians,
both to avoid being identified in the event of persecution and in
order to avoid the impure practices of the pagans.
How exactly, then, Prof. MacMullen wonders, did
Christianity generate those millions of followers in the years before toleration? He suggests an
answer by trying to “imagine in some detail a scene that conflicts
with no point of the little that is known about conversion in the
second and third centuries.”
I would choose the room of some sick
person: there, a servant talking to a mistress, or one spouse to
another, saying, perhaps: “Unquestionably they can help, if you
believe. And I know, I have seen, I have heard, they have related to
me, they have books, they have a special person, a sort of officer.
It is true. Besides and anyway, if you don't believe, then you are
doomed when a certain time comes, so say the prophecies; whereas, if
you do, then they can help even in great sickness. I know people who
have seen or who have spoken with others who have seen. And healing
is even the least that they tell. Theirs is truly a God
all-powerful. He has worked a hundred wonders.” So a priest is
sent for, or an exorcist; illness is healed; the household after that
counts as Christian; it is baptized; and through instruction it comes
to accept the first consequences: that all other cults are false and
wicked, all seeming gods, the same.