You know more about Divine lore than I do so I struggle with them, but their goal is to drive him crazy...
Not crazy, the Amulet is trying to either "A" make him more appealing and useful, "B" try and get itself off of him and to someone it likes more, and "C" make sure he doesn't claim it for himself.
Think of it like the Ring from Lord of the Rings, and think of Cassamir like Gollum or Frodo at this point.