Having being inundated by childrens' books - I have three very busy little ones - one series that struck me was the Magic Treehouse (need to confirm title).
There, there were hundreds of books, and the protagonists would find one was either mysteriously open, or a bookmark had appeared.
By opening the book,looking withing and making any type of statment that could taken as a desire to travel, the treehouse would travel to that destination.
So, this, plus such TV shows as Quantum Leap
Simply put, the book contains many quests - typically wrongs that need righted, appropriate to the party at hand. These quests should be serious - one should not casually peruse this volume.
Apart from the obvious, a means to 'logically' bring the PCs to whatever plot suits your fancy, the book could serve other purposes.
Someone else has been drawn into a quest and the PCs have been somehow involved to find them. After some searching of varying degrees of difficulty, they find the book open to a particular page. They then need to enter the quest, one which is more suited to the missing party then their own...