David Powlison begins his explanation of what constitutes biblical psychology by saying simply that "Christian faith is psychology." Like any worldview, Christianity offers a very distinct "coherent, comprehensive understanding of how people work" and he says that this is "intrinsic to thinking Christianly." Indeed, there is a sense in which we are all psychologists because we all have a worldview and this worldview informs how we view humans and how we interpret how they think. He notes that Jesus, for example, provides a very distinct interpretation of the "thoughts and intentions of the heart." Scripture offers a distinct interpretation of the source, nature and scope of our motives.
We are given a systematic interpretation of how humans ought to flourish, which includes an account of healthy mental functioning. Ultimately, "A Christian understanding systematically differs from how other psychologies explain the same phenomena." Once again, this is true of any worldview. Furthermore, Powlison insists that Christian ministry is itself a form of psychotherapy.
"Intentional, constructive conversation is indispensable to practicing Christianly. The revelation of Jesus Christ creates a distinctive conception of the relationship between counselor and counselee, a distinctive understanding standing of methodology, a distinctive social location for counseling practice to flourish. This care and cure for the soul systematically differs from how other psychotherapies deal with the same problems for living."
Indeed, Powlison notes that the fact that we have our own worldview and that it is a distinctly Christian worldview means that we must think about the psychologies produced with other worldviews and how the psychology of our worldview interacts with theirs. We must challenge them with our own presuppositions but we can also learn from them:
"We share a desire to help make right what goes so wrong in personal and interpersonal life. Yet we see with different eyes and proceed with different intentions. The similarities, analogies and commonalities create reasons for extensive interaction, expecting to learn from each other. The differences, disparities and antinomies create reasons sons for thoughtful disagreement, seeking to persuade each other."
What presuppositions should underlie a distinctly Christian psychology? As Augustine said, Powlison said that we must believe in order to understand rather than the other way around. Failing to believe means that we discard the key to true knowledge and believing incorrectly causes us to systematically distort our perception of reality.
We must believe that humans are the image of God and that we are accountable to God. We are accountable to God for our deviance from his standards, but we can also be renewed by God. For the psychologist, this means that the Christian's mind can be renewed by God. Our psyche's are innately attuned to God, whether we know it or not, according to Powlison. God is the maker of everything. This includes the maker of our brains and of the genes that may have predisposed our genes to behave in certain ways. This also includes various neurotransmitter and hormone levels which may influence our behavior in certain ways. We are totally and utterly dependent upon the Being of the Triune God.
Thus, it becomes clear that we must, as St. Augustine, Powlison and the Bible all declare, first believe the truth of the Christian worldview if we are to be Christian psychologists. We cannot begin with science and hope to reach Christianity, or any other worldview for that matter, since the scientist already comes to his lab with a worldview which precedes it. To think otherwise is to postulate the existence of a totally neutral scientific practice, which is absurd. We all have worldviews, and the worldview of the Christian psychologist must be a distinctly Christian one if he is to operate in obedience to God.