The earliest Christians did not have church buildings. They typically met in homes. (The first actual church building so far found is at Dura Europos on the Euphrates, dating about 231.) They did not have public ceremonies that would introduce them to the public, and they had no access to the mass media of their day. So, how can we account for their steady and diverse expansion over the first three centuries?
After the Apostle Paul, we do not run across many "big names" as missionaries in the first few hundred years of Christian history. Instead, the faith spread through a multitude of humble, ordinary believers whose names have been long forgotten.
Early Christianity was primarily an urban faith, establishing itself in the city centers of the Roman Empire. Most of the people lived close together in crowded tenements. There were few secrets in such a setting. The faith spread as neighbors saw the believers' lives close-up on a daily basis.
And what kind of lives did they lead? Justin Martyr, a noted early Christian theologian, wrote to Emperor Antoninus Pius and described the believers: "We formerly rejoiced in uncleanness of life, but now love only chastity; before we used the magic arts, but now dedicate ourselves to the true and unbegotten God; before we loved money and possessions more than anything, but now we share what we have and to everyone who is in need; before we hated one another and killed one another and would not eat with those of another race, but now since the manifestation of Christ, we have come to a common life and pray for our enemies and try to win over those who hate us without just cause."
In another place Justin points out how those opposed to Christianity were sometimes won over as they saw the consistency in the lives of believers, noting their extraordinary forbearance when cheated and their honesty in business dealings.
When Emperor Julian ("the Apostate") wanted to revive pagan religion in the mid-300s, he gave a most helpful insight into how the church spread. This opponent of the faith said that Christianity "has been specially advanced through the loving service rendered to strangers and through their care of the burial of the dead. It is a scandal that there is not a single Jew who is a beggar and that the [Christians] care not only for their own poor but for ours as well; while those who belong to us look in vain for the help we should render them."
On the surface, the early Christians appeared powerless and weak, they were an easy target for scorn and ridicule. They had no great financial resources, no buildings, no social status, no government approval, no respect from the educators. And after they became separated from their first-century association with the Jewish synagogues, they lacked institutional backing and an ancient tradition to appeal to.
But what finally mattered is what they did have. They had a faith. They had a fellowship. They had a new way of life. They had a confidence that their Lord was alive in heaven and guiding their daily lives. These were the important things. And it made all the difference in laying a Christian foundation for all of Western civilization.
Adapted from Christianity.com Church History.