In the history of the Christian religion there may be no parallel to the Worldwide Church of God’s radical transformation from a marginal sect to a recognized denomination. Formed around Herbert W. Armstrong (1892-1986), the sect became one of the largest religious media ministries, offering the Plain Truth magazine and the World Tomorrow radio and television programs. After Armstrong’s death, the sect was headed by Joseph W. Tkach who, before his own death in 1996, reformed some beliefs and practices. He was succeeded by his son, Joseph Tkach, who renounced the sect’s dependence on Armstrong’s teachings. A significant issue in this transformation was the Worldwide Church of God’s adoption of the Christian Doctrine of the Holy Trinity. The cognitive developmental theories of Karl Helmut Reich, of Switzerland, outlined in his book Developing the Horizons of the Mind (Cambridge University Press, 2002), are related to the application of the idea of complementarity, drawn from quantum physics, to the resolution of paradoxical ideas , with some reference to the Doctrine of the Trinity. The focus of the research was on how these leaders, as change agents, were able to demonstrate development of their thinking, (as gauged by their understanding of the Trinity Doctrine) according to Reich’s stage theory. As the first study of this kind, the results were enlightening and raised hope about the ability of Reich’s theory to explain the phenomenon studied and also revealed progress in the transformation or conversion of Worldwide Church of God leaders. / Doctor of Philosophy (PhD)