Sages and wizards (and me!) like to have piles of books around them to pore over, quote from, argue about.... and on rare occasions let other characters look through them. But unless you are very well prepared, there will come a day when a character turns to the bookshelf and asks what volumes he can find there....
... don't panic, start rolling against the hundred different tomes listed here. And then sneak in a book or two that's relevant to your plotline, that holds the relevant information, without it being too obvious!
Roll a 12, for example, and find "Illusion and Summoning: A Tract" by Susan Taylor the Trifold. You can see the words "Igira kali kini dolibix!" inscribed on the inside cover.... now, I wonder what happens if you say them aloud. What if you said them at midnight whilst burning incense...? Perhaps it's better not to know.
Or maybe you found "The Huge Pamphlet of Flower Arranging and Alchemy" - OK, why those two together? Watch the characters going nuts trying to work it out!
Just plain useful, and entertaining, and... cannot really go wrong at the price!