Chapter 4 is on architecture and is a long one. Vernon compares layered architectures with hexagonal ones, pointing out the advantages and disadvantages of each. He also walks through CQRS (Command Query Responsibility Segregation) and many options for implementing it as well as the pros and cons. He steps into Fabric/Grid Computing as well as a useful feature to use in Event Sourcing.
Here is a good place to note that in the book that are many, many references to chapters farther in the book. This is fair since the book does build on other books and the reader should have at least a knowledge of the concepts being discussed throughout. My suggestion is if you know a little something about these more advanced subjects, continue on as it will all come together in the end. If you really don’t feel comfortable continuing on without further knowledge, go ahead and peek ahead or hit up wikipedia real quick.
Next up: Entities