I think by showing Jack's dad in the cabin, they are implying that Jacob and the smoke monster are one and the same. We know that the smoke monster can take the form of the dead like it did when it stole Eko's brother Yemi's corpse from the biplane and then subsequently took Yemi's form before the smoke monster killed Eko.
What other corpse is supposed to be on the island but vanished? Jack's dad. Then Jack's Dad appears in the cabin when last season, we saw a flash of Jacob in a different form. It's also interesting that in the second episode of this season, Locke asks Ben what the smoke monster is, when the episode before that, Locke is clearly in the cabin talking to Jacob. Maybe that conversation sparked the question when he realized what Jacob is.

