User blog comment:Monkey.D.Me/PUNK HAZARD - FAQ/@comment-4161592-20120215172148/@comment-4132693-20120215222800

Law is known for his brutality. Plus if i remember correctly, appo-san mentioned that there has to be some catch to Law helping Luffy. It may be to get noticed in another manner or woteva he is up to. The Gorosei were very worried after the war with the open seats in the shichibukai, so again, it is possible Law got an offer. Now with Vegapunk being involved and Law DF ability, that does like a solid theory to me...