When the Locke-ness-Monster claims it was trapped, I think it meant he has been a slave to Jacob and the island for a long time... We've seen it be summoned and protect the others and the Temple before. Now that he is free he no longer works for them. I believe the events that have been happening all go in a cycle. I believe Jacob started similar to this. Jacob then had to recruit people (Richard took his place sometimes). After the new Jacob (most likely Jack or Hurley) kills MIB, he/she will have to rcruit a group of people (like what MIB is doing now).