Theologians, philosophers, and psychologists slice man in different ways, and there is no use trying to make the sections coincide.
That is a great quote and true to boot. All three disciplines and their associated words and phrases can be helpful. However…
Psychologists should be wary of dabbling in theology, lest they bite off way more than they can chew.
There have been great Christian psychologists, but not when they got their theology and psychology too mixed up.
Theologians should not be dismissive of psychology, nor scared of it.
Theology and philosophy intersect a lot, but again, they can become too mixed up. Calvin’s Institutes are pretty good when he sticks with the Bible, but can go south at times when there is too much Plato.
Philosopher’s should make themselves a bit more useful by incorporating (or at least being aware of) some psychology. They should also do their homework before talking theology. That homework would include prayer.
After this quote, Erikson goes on to comment on Luther’s theology:
The main point to be made here is Luther’s new emphasis on man in INNER conflict and his salvation through introspective perfection. Luther’s formulation of a God known to individual man only through the symbolism of the Son’s Passion redefined the individual’s existence in a direction later pursued in both Kierkegaard’s existentialism and Freud’s psychoanalysis – methods which lead the individual systematically to his own borders, including the border of his religious ecstasies.
Erik Erikson, Young Man Luther, p.214