The book seems fairly important overall, Gale wants it either to Read or Eat and Astarion wants it to read. And the player character can do a ton of checks for a poor reward right now. I posit that it will become something more and more important over time depending on who you gave it to (unless gale vored it), and it is very possible that as said above it might be meant to grant higher level Necromancy, which is not implemented properly yet except for Speak with Dead.