Christian is the body snatcher
Not the real Christian. People don’t get resurrected. Either Jacob or the other guy is inhabiting Christian’s body-shell-mold. Heck, that’s probably not even Jacob’s real body, maybe the mold-body doesn’t age & that’s why Richard doesn’t – and may explain the ‘dead’ Hurley’s been seeing.
Dave may be to make sure Hurley didn’t show up on the island in the first place (a variable). I’m not sure which one, ‘cuz Jacob appeared to all but Hurley & Sayid before 815, so maybe he didn’t want Hurley around until he knew he had to have him (and that durned guitar case) – or maybe it’s the Rival.
Jacob is the man of faith, faith in man, faith it will all change. The Rival is the man of science who believes the experiment has been recreated enough times to be a real theory/law.
(Of course, Maybe Christians DO get Resurrected.)