Ok let me just say that I am highly sleep deprived, so I am really going out on a limb here.
Jacob tells hurley to take Jack to the lighthouse ( because someone is coming to the island and he wants the
to be able to find it).
When they get to the lighthouse, Jack had yet Another freak out with no resolution. Buy I think the point of getting Jack up there was just to prove to him that he has always been special, not to bring anyone to the island. I think Jacob(being as brilliant as he seems) already knew that no matter what, Widmore knows where the island is (maybe from Mrs. Hawkings or Desmond) and is planning to take over the island as leader again. Therefore he is doing a little "Reacon" of his own.
Maybe I put to much thought into it, but after watching Lost since Day one I have learned one thing, the obvious resolution is usually not the correct one. Jacob said someone was coming to the island, but he doesn't say that this person is someone good. This person (Widmore) might be Jacobs loophole.