There were a few conditions that allowed Christianity to grow and eventually thrive in the Roman Empire. Christianity emerged during the Pax Romana (Roman Peace), this was a time of relative peace in the empire and limited expansion. It was also the time when the Roman Empire was at its height. St. Paul, the apostle, was able to travel throughout the Mediterranean to different parts of the empire with relative ease in order to spread the message of Christianity. The fact that he possessed Roman citizenship was very helpful as well.
Another favorable condition was the fact that Koine Greek was well known among educated people in many parts of the Roman world. Paul and other Christians were able to easily communicate with one another throughout the Roman Empire. Rome's postal service was very sophisticated and reliable for its time and long distance correspondence was commonplace.
