Idea/theory: Jacob and the other guy are gods that play a game with each other to entertain themselves because being gods, they have seen and done it all. When the dark shirt god says to Jacob "You know how bad I want to kill you", he means it in a way that is similar to like check mate in chess and whoever kills the other first wins the game and then it will need new characters to play again. In the rules they must not engage each other directly or reveal themselves to the characters. My guess is the god in the black shirt has not won in a long time and really wants to kill Jacob to win for once. The Island is the chess board and all that happens are within the rules of the game laid out by the gods themselves. They may use any and all means necessary to achieve a victory including psychological manipulation. Think about how many times, even since season one, that games and colors of playing pieces are referenced. Hence all the black and white items on the island. Remember when Jack first found the black and white rock on the skeleton in the caves and when Locke first had the backgammon board on the beach??? What are your thoughts on this?