The revelation of Jacob and the Man in Black in "The Incident" is of course significant on multiple levels, some (or all?) of which may not yet be known. But one of the most important aspects of it is our Losties are pawns. We're not aware what the struggle is, whether a game or something more serious; we are, however, aware of the principle players now. And it seems they are not our Losties.
I have to admit, I really like it this way. They've always been sympathetic characters, but now they're even more tragic. Nothing like pitiful humans in the hands of powerful beings to take things to Shakespearean levels. Only, this time, we were rooting for the pitiful humans five seasons before we discovered they were being played. Now we get to see how they overcome it.