User blog comment:Godisme/Natsu vs. Rogue/@comment-1454981-20130405173339/@comment-7418318-20130405230433

With such a mysterious character like Zeref it's really hard to tell. And neither knowing what will happen if the gate remains open or is closed isn't helping much either.

Assuming the closing of the gate prevents the dragons from invading and if he reverted to his old self, he might just want to make sure he can take the planet for himself, without having to share with the dragons.

Or if he still cares about live, he might want to prevent the dragon invasion to save lives.

If the gate can really work as a cannon to wipe the dragons out, he might want to prevent that so the dragons can wipe out mankind as punishment for their sins.

Hell for all we know he might even have gone completely crazy and believes he can negotiate a peace treaty between the dragons and humans...