This book is packed with profound and practical spiritual truths. Marianne Williamson is writing with deep compassion and obviously has considerable first-hand experience of the principles she's writing about.
The basic message here is that we are all perfect expressions of love, and that the energy of love and God is all there is. Anything else is an illusion. All the judgments of oneself and others, feelings of superiority and inferiority and so on fall away if one chooses a path of unconditional surrender to God's will, that being the truth of who one is. Many practical examples of how to apply this approach are presented. I found the chapters on relationships and work particularly interesting.
As someone who struggled to get to grips with the original "A Course In Miracles" in the 1980s, I thank Marianne Williamson for giving us a more accessible version of the same powerful truths. As with the original text, some people (e.g. me!) may be a bit uncomfortable with some of the use of Christian terminology, but God and God's love are being re-defined here, in a similar fashion to Neale Donald Walsch's extraordinary "Conversations With God" books. Masterful stuff!