I have assumed all along that the island was the one making the decisions. That at different times the island has its messenger. Be it Horace at Ben's birth, be it Richard with Locke at a couple of different times, be it Matthew Abbadon with Hurley or Locke. The emmisarry that the island chooses is important because that person is the best connection to the island. That is why we are looking for the new people I think.