This book contains magical enchantments of witches from the movie, charmed. Those enchantments are for both demon vanquishing and personal gains. In fact, this book has supernatural ability to protect itself from evil whereby only good people are able to touch it or read it.
The book of shadows gets thicker when its owner created new spells. Although the pages can be torn but it leaves no marks and continue to serve its purpose for its owner. Book of shadows is therefore a resourceful book that stored powerful magic. Many demons want it for their power growth. Even the most powerful demon want it.