MArcomage

Shouldn't it say something like "Discard all cards in your hand except Book of Eternity"? Otherwise, the durable keyword would be pretty useless since it would be discarded by the card's effect anyway.

Literally speaking, it would hopefully discard other instances of Book of Eternity on hand. Probably best to just stick the words "all other cards from" in there.

Durable overrides any card effect (discard), so you can't have a card that will discard itself and be durable.

edited as DPsycho suggested

"Discard your hand" is shorter =)