Phenomenal book! One of the best books I've read on spirituality and non-duality, while grounding it in the mechanisms of the ego. I read this after Sandra Maitri's "The Spiritual Dimensions of the Enneagram", which is a more accessible guide to the Enneagram, whereas this book is more focused on the spiritual aspects of it.
The core premise is that if a person is perceiving the reality of "Being" in an undistorted way, as a non-dualistic "unity" (which is elaborated upon by the 9 "Holy Ideas" - nine "facets" that describe "unity"), and perceives oneself and all things as inseparable from this unity, then one will have "basic trust" (an implicit, pre-conceptual trust in reality itself).
But with the development of the ego, a person will lose sight of the Holy Ideas, and develop "Specific Delusions" (corresponding to each Holy Idea), which are distorted egoic perceptions of reality. And with the loss of contact with Being, there is felt the corresponding painful, deficient states called "Specific Difficulties", as well as a loss of basic trust resulting in distrustful "Specific Reactions". The book goes into detail on each of these aspects for each point of the Enneagram.
For those well-versed in Enneagram, this book deviates a bit from the mainstream characterization of the Enneatypes, and especially goes against the idea that a person is strongly defined by a singular type, but rather makes the case that every ego has all nine types within them.