The Pauline letter to the Ephesians and other texts of the early Christ-movement present behavior norms that vary considerably from one text to another. Many of these behavior norms were quite conventional in the first-century Mediterranean world and not unique to the Christ-movement. Nevertheless, the norms are typically presented as expressions of the identity as Christ-believers. Why? How was the relation between social identity and behavior norms constructed in the early Christ-movement? How did the Christ-believers in the early Christ-movement experience their identity "in Christ" as both causing and requiring certain behaviors? The purpose of this study is twofold: Roitto first discusses how the cognitive sciences can provide a theoretical framework to answer the questions raised above. The aim is to provide an analytical perspective that is founded on cognitive research regarding how human minds handle identities and behavior norms. Second, he applies this framework to the Pauline letter to the Ephesians in order to present a new understanding of the letter, particularly of the relation between identity and behavior norms as expressed in the text. In the analysis of Ephesians, Roitto also discusses the potential group-dynamic effects of Ephesians, assuming hypothetically that its construction of identity and behavior norms was embraced by local communities of Christ-believers. In order to demonstrate the broader relevance of the approach in the ancient Mediterranean context and in the early Christ-movement, Roitto also intentionally takes illustrative examples from ancient sources outside of the Bible.