User blog comment:FairyRaven/Fairy Tail Chapters 338, 339, 340: Review and Commentary/@comment-15267891-20130705135438/@comment-7418318-20130705150354

Somehow that last chapter gave me the feeling that Mavis founded Fairy Tail specifically to counter Zeref, should he ever turn his mind to destruction - which he just did.

If Zeref can really turn the world into the horrible place that Hades desired, maybe Lumen Histoire can either block that transformation or revert it.

Imagine it. Mavis creating a great weapon against evil ("Fairy Tails light" according to her) and then builds the guild on top of it to hide it untill it's needed.

As for Cobra, while it's possible he might have meant theother Dragon Slayers, I think he's refering to bring back Oracion Seis (Mangastream even translated it as such "So I can save the rest of Oracion Six"), but the question is, to what purpose.