Spirit of Truth is the first of a two-volume study of the origin and development of the teaching of the Holy Spirit as it appears in the Gospel and First Epistle of John. Scholarly works on Johannine Pneumatology have tended to concentrate on the image of Spirit as Paraclete or Advocate, and have neglected the specific ‘hermeneutic’ or teaching-interpreting role attributed to the Spirit throughout the New Testament and specifically in the thought of the fourth evangelist. The purpose of this study is to explore and explain how this hermeneutic function developed in Johannine thought and ecclesial experience, and to stress its vital implications for scriptural interpretation and preaching within our church community today. The first volume reveals the influence of the Old Testament, Zoroastrianism and Qumran texts on the shaping of the figure of the Spirit in Israel’s religious experience. It traces the origin of the image of Spirit of Truth through the Old Testament and intertestamental Judaism. Its dualistic aspect (‘spirit of truth/spirit of deception,’as in I John 4:6) is shown to be rooted in the Dead Sea Scrolls and, ultimately, in the ethical-eschatological dualism of the Iranian prophet Zarathustra. This book shows, finally, how Israel came to know the Spirit as a blessing, sanctifying, protecting and revealing divine presence.