What if the names on Jacob's wall are those under protection from Jacob. They cannot be directly killed by MIB. Each group of candidates that arrives on the island slowly either end up killing themselves, prove themselves unworthy, or are infected by MIB. Each time a set of candidates is eliminated Jacob has failed in his quest to prove Flocke wrong and the cycle begins anew finally arriving at our current Losties. This would explain why the blonde hair boy in the last episode tells MIB "You know the rules.You can't kill him" as he leads Sawyer off into the jungle. Who or what governing power the boy represents is still unclear. The Black Rock could also have brought another such group of candidates to the island. Maybe somewhere in the cave of names is Jacob's very own name and number from the time that he took over as island protector? Also this answers why MIB can't kill Jacob himself. Im probably way way off base here but let me know your thoughts and objections on this.