Before Constantine issued the Edict of Milan in 313 CE, making Christianity an accepted religion in the Roman Empire, the religion spread in part because its message of salvation appealed greatly to people who lived disenfranchised lives, particularly on the borders of the Roman Empire. Women, children, and slaves were particularly drawn to Christianity, as it promised equality that was not present in the social hierarchy of the Roman Empire. For example, women could serve as deaconesses in the early Christian church.

In addition, apostles such as Paul journeyed across the Roman Empire, preaching to poor people in cities such as Ephesus and Athens, where the poor were particularly receptive to his message. Paul hastened the spread of Christianity by preaching not only to Jews, but also to non-Jews, broadening the base of potential converts. In addition, Christianity relaxed many of the Jewish laws regarding diet and other religious practices, making it more appealing to converts. Upheavals during the third century CE continued to enhance Christianity's appeal, as Rome was rocked by invasions and political problems.

After Constantine converted to Christianity and made Christianity legal, he constructed churches and promoted Christians to high offices. He was a patron of the religion and used the power of the state to spread Christianity. He also provided incentives, such as tax breaks, to members of the Christian clergy. Though Christians still faced persecution after Constantine, Christianity eventually became the religion of the Roman Empire.