User blog comment:FairyRaven/Fairy Tail Chapter 440: God Serena, Review and Commentary/@comment-7418318-20150615161153/@comment-7418318-20150616160407

FTF, maybe he's not after the power at all, but doing it for Mavis' sake.

In Zero he swore that he'd protect Mavis. Maybe he thinks - or it might even be the case - that using Lumen Histoire hurts Mavis in some way and to prevent this he's plotting to play both sides against each other so he can snatch LH away and hide it someplace where it will never be used again.

Or he might think that keeping Mavis in this suspended state of half-death is too cruel a fate and wants to destroy it so that Mavis can be released and move on to the afterlife for good.