An extremely thought provoking book, one that students of church history will be sure to want to read, is Leonard Verduin's THE ANATOMY OF A HYBRID: A STUDY IN CHURCH-STATE RELATIONSHIPS (Sarasota, Florida: The Christian Hymnary Publishers, 1976), also available at

Verduin examines the effects of the drastic changes to the church beginning in the time of Constantine in the early 300s. This book now only clarifies much of church history and the many problems arising in mixing religion and politics, but also the fundamental difference between the testaments. (Whereas the O.T. Israel was a church state and a state church, the N.T. body of Christ is neither.)