Music theory. I'm not claiming I understand it all. I've had many eureka moments when I suddenly realise what or why this thing from years ago is important. I

Music theory. I'm not claiming I understand it all. I've had many eureka moments when I suddenly realise what or why this thing from years ago is important. I think teaching music theory with both what and why (with examples) is essential. I still have haven't found a book that does a good job of it and keeps it interesting. Any recommendations?