User blog comment:WhiteArmor/7/7/777/@comment-178.24.186.37-20130112122027

My guess is, that:

Igneel, Metallicana, Grandine, Weisslogia and Skiadrum were raising and teaching all of their children Dragon Slayer Magic because they knew what the 7th of July X791 would bring with it..And they had to prepare themselfs for that said day..Because there is going to be War and the mass Bloodbath known as the Dragon King Festival (the day where the dragons would bash each other and where Acnologia turned into a Dragon) will hence forth once more. So they knew they wouldn't stand a chance against The Black Dragon In The Book Of Apocalypse alone and had to get some help in form of their Siblings and students to fight beside them. And then at July 7th X777 they disappeared to prepare themselves for the fight.

To Layla:

I think that Acnologia was about to obliterate his enemies and Layla was in contact with the dragons and knew about Acnologia's presence and history. Because she was known as the strongest Celestial Spirit Mage in history, she somehow sacrificed herself through the use of her magic power to transport the Dragons to another place (maybe the Celestial Spirit World) so they wouldn't be harmed until that fateful day as they are their only hope.

To Zeref:

As mentioned by Arcadios, Zeref was the one who turned Acnologia into a dragon. And since Acnologia may have Zeref's magic power within himself, he responds to Zeref's Magic and comes to find whereever The Dark Mage appears. It could also be that Acnologia has still his memories intact and wants to take out Zeref for turning him into a beast. Because as you know Dragons have a very high level of intelligence.. And maybe that's the reason for the upcoming war on July 7th X791 (Acnologia clashes in a fight with Zeref and the Dragons return to take both of'em down at once).

To Acnologia:

By the Way, I think that Acnologia for some reason is/was the Water Dragon Slayer since he sucked up masses of Water for shooting his Dragon's Roar on Tenroujima..

My personal opinion is:

Natsu is without a doubt a damn powerful Dragon Slayer if not even the most powerful human one alive. But i doubt that he is able to kill a Dragon right now..