Believers in Jesus’s divinity met in small assemblies or congregations, often in one another’s homes, to discuss the meaning of Jesus’s message and to celebrate a ritual (later called the Eucharist or Lord’s Supper) commemorating his last meal with his disciples before his arrest. Because they expected Jesus to return to the world very soon, they regarded earthly life and institutions as unimportant. Only later did these congregations evolve into what came to be called the religion of Christianity, with a formal organization and set of beliefs.

The catalyst in the spread of Jesus’s teachings and the formation of the Christian Church was Paul of Tarsus, a well-educated Hellenized Jew. Paul traveled all over the Roman Empire and wrote letters of advice to many groups. These letters were copied and widely circulated, transforming Jesus’s ideas into more specific moral teachings. As a result of his efforts, Paul became the most important figure in changing Christianity from a Jewish sect into a separate religion.

Though most of the earliest converts seem to have been Jews, Paul urged that Gentiles, or non-Jews, be accepted on an equal basis. The earliest Christian converts included people from all social classes. These people were reached by missionaries and others who spread the Christian message through family contacts, friendships, and business networks. Many women were active in spreading Christianity. Paul greeted male and female converts by name in his letters and noted that women often provided financial support for his activities. The growing Christian communities differed over the extent to which women should participate in the workings of the religion; some favored giving women a larger role in church affairs, while others were more restrictive.

People were attracted to Christian teachings for a variety of reasons. It was in many ways a mystery religion, offering its adherents special teachings that would give them immortality. But in contrast to traditional mystery religions, Christianity promised this immortality widely, not only to a select few. Christianity also offered the possibility of forgiveness, for believers accepted that human nature is weak and that even the best Christians could fall into sin. But Jesus loved sinners and forgave those who repented. Christianity was also attractive to many because it gave the Roman world a cause. By spreading the word of Christ, Christians played their part in God’s plan for the triumph of Christianity on earth. Christianity likewise gave its devotees a sense of identity and community. To stress the spiritual kinship of this new type of community, Christians often called one another brother and sister. Also, many Christians took Jesus’s commandment to love one another as a guide and provided support for widows, orphans, and the poor, just as they would for family members.