User blog comment:Omega natsu2/Episode 184: The Country, Until Tomorrow, Review./@comment-7418318-20140602135111/@comment-7418318-20140602221511

That's a really good choice.

The first mentions of the Book were as early as the Lullaby incident and it was mentioned several times sine. We even saw at least one image of it. And even within the arc itself, it's revealed very early that the Demon Gates are Demons from Zeref's book. So the no-spoiler side is definitely covered.

And it would also be quite iconic for the arc.