After reading the excerpt for this book that appeared a couple of months before the actual book, I was expecting a book that was about specific current liturgical controversies (altars, music, tabernacles, etc).
While such issues are addressed, the book is primarily a theological overview of the Mass that everyone should read to develop a deeper understanding of the Mass and worship.
This book is not a nitty-gritty "let's look at the rules" type of book. This book has a much higher goal - a survey of liturgical theology and its place in the spiritual and historical context.
The book begins with an analysis of a theory from the early part of the 1900's which posited that the liturgy was a form of "play" He analyzes how this notion falls short and that the Bible holds the key to understanding what liturgy really is.
Through a detailed look at the story of the Exodus and the theology of sacrifice, Cardinal Ratzinger shows that liturgy is inseparable from the worship of God and any attempt to separate the two destroys liturgy.
Following the explanation of sacrifice in the Old Testament, Ratzinger shows how Old Testament sacrifice is merely a foreshadowing of the perfect sacrifice of Christ in the New Testament.
The next section of the book addresses the more concrete aspects of worship including church buildings, music, altars, vestments and gestures but does so without getting into details about liturgical law. It must be kept in mind that the purpose of this book is not to rehash liturgical law but to show the theological underpinnings for the liturgy and the concrete things that are a part of it.
For example, when Ratzinger discusses kneeling he doesn't address current law but instead shows the Biblical roots of kneeling and how those roots should translate into practice today.
The Spirit of the Liturgy is not a quick read. It is not a summary of Church law. It is much more and of much more benefit to the faithful. While it is easy to know what the Church asks and teaches, knowing why the Church asks and teaches is a much more difficult matter. This book does a wonderful job explaining the why of the Church concerning the liturgy.