This study investigates why "faith" ( ) was so important to early Christians that the concept and praxis dominated the writings of the New Testament. It argues that such a study must be interdisciplinary, locating emerging Christianities in the social practices and of contemporary Judaism and the early Roman empire. This can, therefore, equally be read as a study of the operation of in the world of the early Roman principate, taking one small but relatively well-attested cult as a case study in how micro-societies within that world could treat it distinctively. Drawing on recent work in sociology and economics, the book traces the varying shapes taken by in Greek and Roman human and divine-human relationships: whom or what is represented as easy or difficult to trust or believe in; where pistis/fides is "deferred" and "reified" in practices such as oaths and proofs; how is related to fear, doubt and scepticism; and which foundations of are treated as more or less secure. The book then traces the evolution of representations of human and divine-human in the Septuagint, before turning to in New Testament writings and their role in the development of early Christologies (incorporating a new interpretation of ) and ecclesiologies. It argues for the integration of the study of with that of New Testament ethics. It explores the interiority of Graeco-Roman and early Christian . Finally, it discusses eschatological and the shape of the divine-human community in the eschatological kingdom.