User blog comment:FairyRaven/Fairy Tail Chapter 407: All for My Demise, Review and Commentary/@comment-25405856-20141102220009/@comment-7418318-20141102224004

The Dragon Slayers had pretty much no chance at all at defeating him. Why would he lie in a situation like that?

And they need to use Face in order to free E.N.D. Right now END is sealed and none of the Demons is able to break this seal, but since the seal is magic, firing Face will dispell the seal and free END.

As for why they need END to kill Zeref, we can't really tell. But from his words to Natsu my guess would be that only END has the power to kill Zeref, even if he doesn't fight back.

And I think sacrificing Kyouka, who couldn't even defeat Erza, to free master END is a good bargain.