The idea that Jesus Christ becomes the Lord of humankind and takes them into his service is essential to Ernst Käsemann’s understanding of Pauline theology. Over decades, Käsemann’s work concerning the theology of Paul the apostle was dominated by the concept of the reign of Christ and his lordship. This idea also laid the foundation for Käsemann’s understanding of Pauline anthropology and soteriology, as well as for Pauline ethics, ecclesiology and eschatology. However, especially in regard to his understanding of Pauline ethics, one can recognize significant shifts in his interpretation over time.