This scholarly work records the time from the earliest Christians to the Council of Chalcedon in 451 AD. Having a vast radius it covers various important theological thoughts, specifically in relation to the Trinity, atonement, and the sacraments. This book is meant to provide better understanding of the history of the Church, its doctrines and the development of theology of the Christian faith. Contents I. Christian Doctrine in its Simplest form, II. The Theology of St. Paul and St. John, III. Christian Doctrine from A.D. 90 to A.D. 180, IV. The Apologists-Montanism-Irenaeus and Tertullian, V. Early Alexandrine Theology-Controversy with Monarchians, VI. Doctrine of the Sacraments before A.D. 325, VII. Arianism and the Divine Nature of Christ, VIII. The Union of the Divine and the Human Natures in Christ, IX. St. Augustine and the Athanasian Creed, CHRONOLOGICAL TABLE, INDEX, Leighton Pullan (1865–1940) was a lecturer in theology at St. John’s and Oriel Colleges, Oxford. His works include The Atonement, The History of the Book of Common Prayer, The History of Early Christianity, Early Christian Doctrine, and The Church of the Fathers.