The argument between Jacob and his rival at the beginning of the episode implies that they have very different goals when it comes to the island. Jacob seems to want to bring certain people to the island and save them; his rival seems to have a more violent and judgmental disposition. This ties into Richard's answer to Ilana's question: "Who lies in the shadow of the statue?" His answer, in Latin, was "he who will protect us all" or "he who will save us all"
It also appears to tie into the mural on the wall in the Cerberus chamber in "Dead is Dead". A theory after that episode was that Jacob was Anubis, or at least an analogue to Anubis. He seemed to be controlling Cerberus. But what if the mural representing Anubis and the smoke monster is a reference to Jacob's rival? Perhaps the smoke monster is just an extension of whatever Jacob's rival is supposed to be. Was Anubis in opposition to Sobek? This would make sense of the seeming association between Cerberus and the one who takes the form of the dead on the island.
Whatever the case, as seen in the episode, Sobek carried the ankh, a symbol of opposition to evil and the ability to cure diseases. Both seem applicable to the island and Jacob. Sobek was also known to have a distant role in affairs, guiding and pushing others to act in his stead. Whatever the case, this explains the Others a bit more. Jacob selects those who he wants to protect. Richard, who apparently has known Jacob for a very long time, appoints a leader for the actual tribe. That leader does whatever it takes to protect Jacob's chosen. Why they are chosen seems to be the real question, and one that still has no definitive answer. It may, however, have something to do with the redemptive aspects of the series.
It may also be telling that Jacob interacted with Jack, Kate, Sayid, Sawyer, Locke, Hurley, Jin, and Sun at various key moments in their lives. Why were they particularly important? It does vaguely suggest that their survival of the Oceanic 815 crash was no accident, something often hinted in the first few seasons. It's interesting to note, however, that they weren't initially on the lists compiled by Ethan and Goodwin after the crash.
Jacob also interacted with Ilana, which means that all the hints and suggestions that Ilana and her crew were working for the wrong side was more of that misdirection. It would seem that the cabin was actually where Jacob's rival was being "contained", not where Jacob was being imprisoned. That leads to the obvious questions: when was he thus imprisoned and by whom?
It also seems obvious that Jacob's rival was the one who was manipulating Locke and the Oceanic 6 all this time, and perhaps Charles Widmore as well. The war between Ben and Charles could be seen, in context, as a reflection of the larger struggle between Jacob and his nemesis. Logically speaking, it was therefore Jacob's rival that pushed Locke to move the island. Since this led to his ability to take on Locke's form and, presumably, kill Jacob, this all seems to be one massive plot to take control of the island. And it also explains why this period in the island's history is particularly important.