A classic study tracing how Gnosticism emerged as a response to Jewish apocalyptic disappointment after the fall of Jerusalem. This book examines historically and theologically how this belief system influenced and challenged the development of early Christianity. It explores the complex relationships between Gnostic, Hellenistic (Greek), and Judaic thought, and how these elements were assimilated into the formation of early Christianity. Key points in this book include the historical context (The author argues that Gnostic views developed from the remnants of shattered eschatological hopes after the destruction of Jerusalem, which led some to seek salvation beyond this material world), the influence on Christianity (The book analyzes how early Christian figures and communities interacted with, absorbed, or rejected Gnostic teachings (such as dualism and secret knowledge/gnosis), and the source material (This revised edition includes frequent updates based on the discovery of manuscripts from the Nag Hammadi library, which provided direct access to translations of original Gnostic texts such as the Gospel of Truth). This book remains one of the fundamental references for academics and theologians to understand the intellectual background and the heretical challenges facing the church in the first three centuries AD.