Perhaps Jacob and his nemesis are angels? And they have been banished to earth, the island in particular. Jacob is inherently good and the nemesis bad. They have the ability to go "to and fro" between the island and the rest of the earth visiting our beloved Losties guiding their fates for their own "game" . I know some viewers do not like the biblical overtones, but they are so blatant ---I’m thinking in particular the Room 23 brainwashing video Carl was forced to watch, the “God loves you as he loved Jacob” part---. Also, I looked up the Wiki definition of the game backgammon and it seemed to apply to our island crew now that we have the new information from the finale. And I’m betting the white flash was both a time jump and an explosion. Since the explosion was deep underground the effect to the island above will be minimized. Season 5 has left me reeling.