This reveals who Rey is. It is a HUGE spoiler though so do t open if you don't want to know.
http://comicbook.com/2015/12/24/reys-identity-possibly-revealed-in-star-wars-the-force-awakens-d/
I think Rey is Luke's daughter and he sensed she was powerful but leaned to the dark so he dumped her on a remote planet so she couldn't learn the ways of the force. She will turn to the dark side. Luke did not look happy to see her.