This book is setup like a textbook to teach the reader how to interpret the hidden meanings that J K Rowlings inserts cleverly into all the Harry Potter books. 5 keys are used for the explanation.
After being tutored in narrative misdirection, the reader is sent to Alchemy 101 where you learn about the cycles of the series, the imagery, and the themes that carry through all the books. Finishing this course, next you move on the Hermione's favorite - Arithmancy.
Here the reader is educated in the balances that are needed with 4 being magical.
Harmony is needed in the 4 Houses at Hogwarts, 4 Horcruxes have to be found and destroyed by Harry, and 4 magical species (wizard, elf, goblin and centaur all represented in the Fountain of Magical Brethren destroyed in Order of the Phoenix) need to be united.
The reader is also taught that Alchemical works are in three stages - Black, White and Red. The black stage was highlighted in Rowlings' literary works by the death of Sirius Black. The white stage shows the purification of the characters and culminates with the end of Albus (white in Latin) Dumbledore. Are we then to expect danger for Rubeus (red) Hagrid in Book7?
Afterward we learn that Harry and Voldemort are twin opposites.
Harry has his Gryffindor spirit and the Slytherin horcrux scar while Voldemort is the Heir of Slytherin and bodily a Gryffindor because of the blood used at his rebirthing. Harry is the white side being pure of heart while Voldemort is the black side living in his own hell.
We are then reminded of the "hero's journey" in each book how Harry escapes #4 Privet Drive and his task to accomplish is defined.
Prejudice also is addressed when the author reminds the reader of the differences that are brought to the forefront in each book. We are reminded of the different treatments received by PureBloods(those that are poor vs. rich), half Bloods, and Muggle Born wizards as well as the differences in the magical species (wizard vs. elf, goblin and centaurs).
The five keys are then used to created SWAGS (Scientific Wise A-- Guess) for what will happen in Harry Potter and the Deathly Hallows.
All in all, this was a very enlightening book and of all the books I have read on understanding the phenomenon and the hidden imagery, this was the best.