User blog comment:Safaia Mukade/my questions/@comment-6152051-20131019194538/@comment-7418318-20131019222823

Some idiots later came up with the idea that he's dead and cooked up a ritual to revive Zeref (-> Tower of Heaven cultists).

Some other idiots came up with the idea that Zeref is asleep or sealed and the keys were needed to wake him up (-> Grimoire Heart)

Neither of those two ideas has any truth in it, since Zeref never was asleep or dead in the first place. The truth is as follows:

He has a problem with his powers and something of a split personality (that's not exactly it, but it comes close enough).

He only has full control of them while he's evil and while he's good his powers sometimes slip out by themselfs, killing everything in a few meters around him.

But since he doesn't want to kill while he's good, he hid away from the world so he wouldn't accidentally kill anyone.

Most likely he just ran away without thinking to bring his library along.