Jacob is Horace
Alot of people have said that Jacob is Locke, Jack or Christian but I don’t think I’ve ever read anywhere that Jacob is Horace.
So here’s what I think:
Horace is Jacob and when Locke saw him building the cabin he was building it for himself.
Ben knows that Jacob is Horace but hasn’t told anyone. Horace doesn’t use Jacob as a name, it’s a name that Ben made up to fool everyone. There is no such person as Jacob, it is just simply Horace.
Horace needs Lockes help and so tells Christian to tell Locke to move the island. Moving the island will reset the time and Horace will be free again. He will change history and make Ben suffer for locking him up in the cabin.