I hate to be pitching for the other team, but ... an argument is used by christians very often, that's not as simple as it sounds, and frankly, a bad argument.
the argument is basically "Christianity grew REALLY REALLY fast, and it wouldn't have grown that fast had Jesus not rised from the dead." that's a bad Version of it, but the argument follows basically that line.
Now Christianity went from a rag tag bunch of messianic nobodies in palestine, to being about 8-10% of the empire by the time Constantine came into Power. That's a HUGE Growth.
But there are ways to explain it outside of "Jesus must have risen" Now he DID rise from the dead, I believe that, but the rapid growth is not really proof of that, heres why.
By the time Jesus was born Judaism was about 10% of the empire .... Judaism was HUGE, and super popular, especially in the dispora, you had all sorts of People converting to Judaism or becoming "God fearers" or "noahides" even People quite high up in Power.
Why was it so popular?
Well Pagan religions and Judaism were 2 completely different kinds of Things.
Paganism was basically you had Your gods .... they had temples, you went there when you needed something, gave a sacrifice, and then hope you got what you needed, then there were myths around the gods, where they came from, what they did, and so on.
The Gods were almost blessing vending machines, they had nothing to say about the origin of anything, the universe, morality, history, nothing, they didn't tell you how to live, what was right, where Things came from, where Things were going, and also religion was primarily an upper class Things, poor People had local myths and supersticions, but the temples and gods were primarily imperial and for the ruling class. (so in a sense you could say that ancient pagan societies were less religious than modern western societies). For other aspects of life you went to philosophy.
Judaism was WAY different, their God explained everything, where the universe came from, where we are heading, it explained history, it explained morality, and it explained how to live, not only that but Judaism had a social welfare infastructure, so poor jews got help at the synagogue ... pagans didn't, Jews living a good life very often, they had an extremely Advanced religion morally, socially and philosophically ... so a ton of People were drawn to it ....
But whats the biggest problem With becoming Jewish if you're a pagan? Circumcision and the mosaic Law ... but EVEN WITH THOSE stipulations, Judaism grew exponentially under the Roman empire.
Then Christianity comes .... and it grows first in Palestine as a messianic movement, (there is an arugment there for the ressurection), but then it grew extremely fast outside of palestine, very fast, among non jews, InFact it grew faster among non jews (at least in teh second Century and later) than it did among Jews, why? Well basically it was Judaism, without the Law and without circumcision ... so if you were attracted to Judaism before, but were turned off by the laws and getting Your Dick snipped, well, here's Judaism without that, and it also has a further benefit, a kind of revolutionary New Kingdom of god, an escatology that was universal and NOT palestine based (unlike Jewish escatology which was not universal).
OF COARSE Christianity is going to beat out the pagan religions, the pagan religions were simply outdated, they had no social welfare aspect, they had no moral aspect, they had no cosmic narrative, they had no escatology, they were not theologically thought out.
The People who joined christianity from paganism had never probably heard of the historical Jesus, nor was that the driving factor, the Heavenly christ and everything that came With the christian faith was the driving factor.
in the first Century Christianity was one of the only forces providing social welfare for the poor, (as well as Jews), and the only force which was truely universal, and cut away Barriers of race and ethnicity and class, it was a evangelical religion (unlike judaism, which grew hugely anyway), it was the only religion which had a set narrative of history and the universe, which was intellectually satisfying, and it was the only one With a real hope.
So that's what explains the huge Growth of christianity, basically the same thing which explained the huge Growth of judaism before it, along with the perks christianity has that judaism doesn't.
