This book does not offer a linear history of Christianity during the first centuries ce but attempts to show how Christians met the expectations and challenges of their environments. I am perhaps exceedingly cautious in my analysis of the social history of Christians because the rather qualitative evidence of the sources on the individual actors does not seem to me to provide a sufficient basis for quantitative analyses. In addition, I do not give an explanation for the success of Christianity but offer many reasons why Christians were successful in certain contexts.

It is striking that Christians were so successful. They had internal dissension; lacked relics; had no common temple; came from less educated classes and the periphery of the empire; Jews and pagans harassed, even persecuted them. Because they did not offer sacrifices, excluding them from offices and festivals, and were unable to maintain certain family traditions they appeared antisocial. Yet Christ-followers succeeded in winning over non-Jews as well. The persecutions welded Christians together, and martyrs served as role models, even to those who had manifested weakness. In areas such as sexual morality, Christians sought to demonstrate that they were superior to contemporaries of other faiths. They also formed transregional networks. The opportunity to gain prestige in Christian communities also attracted people. Various forms of authority competed with each other, especially the charismatic and spiritual authority of those who excelled in ascetic practices. That in the end monarchical bishops were to become the decisive figures in Christianity was by no means clear from the beginning. That Roman emperors would support Christianity was an unlikely development that changed Christianity significantly. But the tradition of a defiant piety that defined the beginnings was not lost, so that Christianity continued to renew itself.

Christians oriented their lives towards the expectation of a life in the hereafter and yet had to orient themselves in this world. This resulted in very different attitudes. While some were fundamentally anti-family or, rather, against sex in general, others thought about what it meant to have a Christian marriage. While some wanted to participate in the pleasures of everyday life, others rejected this. All tried to live a humble life and do good works, especially towards the poor, orphans and widows. Penance was an institution that allowed Christians to be absolved of their sins, but it also allowed bishops to gain power, albeit in varying degrees Therefore, the question of a Christian way of life was always controversial.

Very few Christians rejected the Roman Empire in principle; rather, many saw it as a prerequisite for their mission because of the peace that the Empire created. Nevertheless, conflicts arose: Few understood why Christians, who worshipped only one God, did not want to sacrifice. In the eyes of contemporaries, this could provoke the gods and endanger social peace, and was a reason for persecution in many places. Many Christians made sacrifices under pressure, but some also became martyrs who gained great prestige. Meanwhile, some Christians entered the service of the state and held public office or became soldiers. They often made compromises that strict Christians criticised. Some seemingly enjoyed the glamour of public duties. That Christians would dominate the empire was by no means a foregone conclusion even at the end of the third century, at the time of Constantine the Great.

Since late antiquity, bishops have been regarded as possessing the highest authority among Christians. But there was no linear path leading there. Rather, there were different bearers of authority among Christians: James, as the respected brother of Jesus, was a key figure at the beginning; intellectuals were able to gain importance as teachers, prophets also appeared after Jesus, among them many women; widows and virgins attained a special position; finally, the authority of ascetics increased. Basically, authority could be derived from an office within the church or from personal charisma, which was considered God given. Good bishops tried to combine both, but charismatics could always challenge them and would continue to do so throughout the history of Christianity.