[Some more from the draft of an article on the psychological effects of the Fall and whether common grace can provide a sufficient response]
Indeed, Pelagius held that the human will is wholly within one’s own power. While the matter under consideration is particularly the question of whether one can lead pleasing to God, do not fall prey to the mistake that the ability to obey God’s law is some sort of bare behavior or “spiritual” decision which does not affect the rest of the person. True obedience to the law of God requires one’s conduct, cognition, affect and will. Accordingly, the ability to obey the law entails a properly functioning psychology.
In his letter to his “Letter to Demetrias”, Pelagius writes:
When I have to discuss the principles of right conduct and the leading of a holy life, I usually begin by showing the strength and characteristics of human nature. But explaining what it can accomplish, I encourage the soul of my hearer to the different virtues.
He explains the strength as an absolute liberatarian freedom of will, “You should not think that humanity was not created truly good because it is capable of evil and the impetuosity of nature is not by necessity to unchangeable good…The glory of the reasonable soul is located precisely in its having to care a parting of the ways, in its freedom to follow either path.”
If the power to do good lies within the human will, why then do any follow a corrupt path. It is not any inherent original sin which has perverted the human psyche: rather, it is the result of sociological and psychological patterns gained from the environment. “Doing good has become difficult for us only because of the long custom of sinning, which begins to infect us even in our childhood.”
Conversely, the manner of becoming “good” is a process of cognitive-behavioral psychology; granted Pelagius was rudimentary in his development, but he was on the “right path” (some might say): “If you therefore you want your way of life to correspond to the magnificence of your resolution …. Apply yourself now so that the glowing faith of your recent conversation is always warmed by a new earnestness, so that pious practices may easily take root during your early years.” (In short be mindful of what you think and what you do, so that through repetition you may become what you resolve to be).
The transformation of the human life is contingent upon God granting a new nature; rather, transformation is a matter of the right therapeutic practice.
 Matt. 5:22 & 5:28, 21:28-32, 22:36-40, 23:28; John 3:16, 14:21; Acts 2:38; Rom. 10:8-17; Col. 2:8; et cetera. “True religion, in great part, consists in holy affections.”Jonathan Edwards, Religious Affections, ed. John E. Smith and Harry S. Stout, Revised edition., vol. 2, The Works of Jonathan Edwards (New Haven: Yale University Press, 2009), 95.
 Again, I am using the word “psychology” deliberately to push back against the idea that there is some “spiritual” aspect of a human being which independently of one’s psychological state. Pelagius is quite right to put the full power to obey the law of God within the human being’s psychological being, his capacity, volition and action. No honest atheist would hold that a Christian’s belief, affection, conduct and volition toward God are somehow divorced from the Christian’s psychology. The atheist may think the Christian diseased, defective, neurotic or whatnot. But only a Christian trying to preserve some sort of fictitious barrier between religious/spiritual life and psychology would attempt such a thin
 J Patout Burns, ed., Theological Anthropology, ed. and trans. J Patout Burns, Sources of Early Christian Thought (Philadelphia: Fortress Press, 1981), 40.
 J Patout Burns, ed., Theological Anthropology, ed. and trans. J Patout Burns, Sources of Early Christian Thought (Philadelphia: Fortress Press, 1981), 42.
 J Patout Burns, ed., Theological Anthropology, ed. and trans. J Patout Burns, Sources of Early Christian Thought (Philadelphia: Fortress Press, 1981), 50; Benjamin Warfield, “Augustine and the Pelagian Controversy,” in Studies in Tertullian and Augustine (Grand Rapids: Baker Books, 2003), 295 (“It was only an ever-increasing facility in imitating vice which arose from so long a schooling in evil; and all that was needed to rescue men from it was a new explanation of what was right (in the law), or, at most, the encouragement of forgiveness for what was already done, and a holy example (in Christ) for imitation.”).
At this point it must be noted that modern psychology would often include a substantial element of physiology: disease of the central nervous system and its effects upon thought, emotion and conduct (whether there such thing as volition in such a regime of pure physiology as a cause, I will leave for others to debate). There is no dispute that the central nervous system can be diseased, and that such disease will have substantial obvious effects. The decay and death of the body are promised results of Adam’s sin. Gen. 2:17 & 3:19. No one disputes that various drugs can and will affect one’s psychology. Drawing a precise line between what is physiological and what is psychological are extremely difficult for everyone involved. There is also the question of responding to one’s physiology (unless with a materialist, there is something more than the brain at issue)