Roughly, the book has 2 parts. The first deals with the history of chess. While the second part is a collection of essays about other more modern aspects of chess.
The history is perhaps the main focus. It has certainly been covered before in other texts, and at greater length. Here, you get a good synopsis of how chess originated in India. Most notably, pawns could only move one square at the start. Hence the naming of Queen's Indian and King's Indian for 2 of black's defenses in the modern game.
We see how chess migrated to the Middle East and thence to Europe, where it slowly changed into its current form. There seems to have been a consensus in the 18th century that stabilised the moves into what was seen as producing a good game, in some esthetic sense. To this day, that consensus has been upheld. Variant moves have garnered little traction beyond mere curiosity value.