"Integration of psychology and Christianity is a very new concept. Yet relating Christianity to the thought forms and intellectual understandings of a society and culture is not new at all. As early as the second and third century, the Christian apologists and philosophers were integrating Christianity with Greek philosophy and thought and interpreting it to the intellectual world in which Christianity was born. (Psychology and Christianity: Integrative Readings - See Selected Bibliography)
There was an antirelgious bias on the part of some significant early psychological thinkers. The most prominent was Sigmund Freud, the founder of psychoanalysis, who viewed much, if not all, organized
religion as an expression of neurotic tendencies, and J.B. Watson, the founder of behaviorism, who viewed the concept of mind, soul, and spirit as unscientific. This bias inhibited the development of an integrative perspective because many Christians felt the field of psychology was itself anti-Christian, and therefore to be avoided.
Integration does not mean the fusion of psychology and Christianity into a third discipline. Nor is it the reduction of Christianity to psychology, creating psychologized Christianity or the reverse, Christianized psychology. In addition, integration is not lining up psychological and Christian concepts or experience, such as the id and original sin or unconditional positive regard and love, and calling the result "integration". All these approaches can be found somewhere in the history of the psychology of religion, but none of these approaches is integrative. As well, integration is not relating a theory with Christianity.
Theory is a part of psychology. It is an attempt to organize the data or parts of psychology into a coherent system. Thus, as part of psychology, these theories need to be examined and related to Christianity as part of the integrative task. Any student of psychology who is also a Christian is aware of psychologists and their theories which appear to be in conflict with Christianity. Also, there are many Christian thinkers or preachers who are antagonistic to psychology.