Lessons of the Zulkir

If you spend 48 hours over 10 days or fewer,
studying and practising the books contents, either
your Intelligence, Wisdom or Charisma can be permanently increased by 1. This can't take you
over the maximum of your score.
If you increase an ability score after completing
the book, you will permanently gain vulnerability
to Radiant damage. If you ever gain resistance to Radiant, you will take 1d8 Force damage every 30 seconds until you die.