It should be obvious by now but...Makarov broke up the guild to hide Lumen Histoire. After seeing Zeref's END resurrection magic, we're led to believe Mavis is waiting to be resurrected too (at the cost of a life, which Makarov regretted not having the courage to do.)
Hiro used Ivan (Raven Tail) as a cookie cutter bad guy after something powerful to indicate its significance to the central plot. Mavis disagreed with him on the nature of LH, but do you understand why he called it FT's darkness? All the Zeref fever seems to be caused by an obsession with resurrection, which is forbidden by the FT world gods. So to Ivan, FT has crossed the gods themselves. (Makes sense for Makarov to want everyone's minds wiped.)
But the gods are the real devils of the FT mythos. Mard Geer explains the One magic split into different magics, such as curse power -- which Ankhseram used on Zeref -- which feeds on evil feelings. Notice Mard Geer assumed END made curse power possible, but recent chapters show that's not the case, even though Hiro hasn't explained. We know Zeref's curse is a central plot point, because it shows the presence of a greater antagonist than Acnologia.
But also pay attention to the symbolism of the primary actors. FT represents civilization concepts like freedom and self-determination, and gods represent all-powerful rulers and conquerers: natural enemies. So that's the conflict the author is writing a theme about.
Tartaros' demons are symbolic of men trying to become gods (power, immortality, etc.). So curse power itself is the magic of gods. Meaning magic in the world suppresses not just curse power but the gods. So that's the context for Mavis's original strategy to start Fairy Tail.
Zeref may play villain for this arc, but Fairy Tail's not done until Mashima says what he wants to about the value of life.