It seeems like the most significant family of Lost is the Sheppard family.
The Sheppard family is the only family that spans 4 generations on the show.
Ray Sheppard -> Christian Sheppard -> Claire Littleton -> Aaron Littleton (yes, I know Jack is Christian's son, but he has no descendants so he does not apply here).
All members of this lineage appear on the show at least once. Is it possible then that Jacob is Ray's father and as a result Aaron's great-great-grandfather in LOST? After all, Jacob is Aaron's great-great-grandfather in the Bible. That would also mean Jacob is Jack's great-grandfather.
I would suspect we will see a flash forward into the future with Aaron, as an adult, making a return to the island similarly to other characters that were born there (e.g., Miles, Charlotte, etc). Maybe Aaron is the key to redemption for this enigmatic and troubled family. Jack's ultimate purpose could be intertwined here as well.
If this has already been discussed on the blog, forgive me.