I read through a lot of the other theory threads but didn't see this come up. There a lot of Old Testament stuff in here, and I would be glad to explain a lot of it if asked (not a scholar, but feel comfortable enough).
Jacob was the grandson of Abraham (who had the original covenant with God in the OT) who stole his older brother's (Esau) birthright from his blind father. He fled his homeland and came to a river where he took a nap. In the dream he had a vision of a ladder going up to heaven where angels went back and forth between heaven and Earth.
The vision prompted Jacob to make God his God and he went on to be the father of 13 boys who all the tribes of Israel were named after. His 12th son was a boy named Joseph who could see the future and was eventually entrusted as the governor of Egypt. His last son was Benjamin and was his favorite.
Jacob was also the only person in the OT that God was quoted as saying that he "loved". Even though he did lots of bad things (stealing his brother's birthright) God still favored him and damned his brother Esau.
We now have references on LOST to Jacob, especially in Room 23 where Karl was being held where on of the slides reads "God loves you as he loved Jacob" or something to that extent. The other 3 slides were allusions to Buddhist teachings but also matched lyrics from Led Zepplin songs. One of Led Zepplin's most famous songs was "Stairway to Heaven".
Jacob also appears to be the leader of one group of Others on the island, and also has a second in command named Ben. One group (Ben's group on Alcatraz) is civilized and is working for something. The other group seems less civilized (walks around in the jungle barefoot, stole Tailes?) and has much less of a known motivation. This mirrors the two tribes of Jacob and Esau from the Bible.
The island is obviously special (the electro-magnetic field, it's healing abilities, it's inability to be seen by the rest of the world, the Black Rock, the giant 4 footed statue) and is well protected by the Smoke monster. (security system) What if the island was some kind of staging area between the real world and the supernatural?
Not Purgatory, but an open door. Angels, both good and bad, can take on many forms. This would explain why everyone sees things that obviously aren't there, but they know of (Jack's father, Kate's horse, Dave, Walt) and why there are so many people with prophetic visions (Locke with Boone, Charlie being told to protect Aaron, Desmond being able to see the future) but in the Bible both Angels and Demons have access to the world. That would explain why so many bad things happen (Shannon following Walt and getting shot, Eko seeing Yemi and getting smashed) almost like a war between good and evil.
This foreshadows something much bigger that I can't really explain a reason for but just have a hunch about. The island is a staging area for the armies of good and evil and the Losties/Others will produce both a Christ-like Messiah and an anti-Christ.
Dharma (as revealed in the ARG) is discovering a countdown to when the world will end and must stop it. They are trying to genetically engineer a Messiah (Juliet and the foreshadowing of a virgin birth through her work) to save the world. But what if the real Messiah (Aaron? Sun/Jin's baby? Walt?) was already on the island?