I'm tearing my hair out trying to get the Priest Spell Avatar from Khoth's cave. What does it want from me?

[GiveMeAvatarAlready]

"You find a book that seems to contain some sort of magical instructions. Unfortunately you can't make any sense of them. Casting a spell you don't understand is always more dangerous than not casting it at all. You replace the book on the shelf".

 

This is the message I get when I'm at the bookshelf that supposed to teach me Avatar, instead of the "Congrats, you now know Avatar!" message or whatever. I have only two characters who can do Priest Spells, one of whom is up to Level 7 already, and one who isn't. What in the blue blazes do I need to do to get this spell?! Do both my Priest-casting characters need to be L7? Do I need to increase anyone's intelligence? 

[Misc Staple]

Your mage lore may not be high enough, though that's just my guess.

[Quiconque]

Yeah, definitely Mage Lore.  I think some of the level 7 spells go up a little above 20 required -- it counts the party's Mage Lore in total.

[GiveMeAvatarAlready]

Ahh, thank you! I'll try increasing and go from there.

[GiveMeAvatarAlready]

That was it! Needed 20 mage points.