Christianity was at first a Jewish sect.It really surprises me how they managed to spread so much. How did they convince the pagans to convert to Christianity? What made it so successful in spreading?
I answered a question very similar to this a few days ago! My answer dealt more with the spread of Christianity as a whole, but I emphasized the Roman period of Early Christianity.
One of the references I made was an answer by u/midwesternphotograph, they answered a question almost identical to yours.
The answer given by u/TheDevilsAgent in this thread is also a good, concise account.