In the Bible Isaac and Rebekah had twin sons named: Jacob and Esau. Jacob and Esau were the 1st pair of twins and according to Genesis 25:21-26 they were fighting in the womb. Jacob and Esau were famous for starting the tribes of nations.
In Lost Jacob and his Nemesis (Flocke, MIB, Esau, etc. I will refer to him as Esau) represent the fighting between the biblical versions of these characters. Right now Jacob and Esau are trying to gain as many followers as possible to create their own tribes. Possible setting up a battle between the two in the end. This also intersects religiously with the concept of good vs. evil. Jacob being good and Esau being evil (obviously).
It also, which I recently realized intersects with the Taoist concept of balance. This concept consists of light balancing out dark, evil balancing out good, etc., but when one of these sides are eliminated, the balance is lost and chaos breaks loose. With the death of Jacob (good) there is now nothing to balance out Esau (evil). That is why Jacob is in hot pursuit of a candidate which are currently: Jack, Sayid, Hurley, Sawyer, one of the Kwon's. As of right now it looks like neither Sayid nor Sawyer will be candidates for the good as they have sided with Esau. That leaves Jack, Hurley, and Sun or Jin. Jack is definitely the favorite to take over for Jacob because one, Jack has been a leader throughout the whole show. Two, Jack and Locke have balanced each other out throughout every season (Man of science vs. man of faith).
I cannot wait to see the rest of the season and how all of this plays out.