Mother takes Jacob to The Source/The Light, passes her job on to him

Mother returns to the caves at night where Jacob is sleeping. She wakes him and tells him "It's time." She leads him through the jungle and as they're walking Jacob says that "Something happened, didn't it?" She tells him that she had to let MIB go because she doesn't have a choice and it's what he wants.

As they reach a stream, she asks him if he recognizes where they are and he does. It's the stream that leads to The Source, the tunnel of light. She passes Jacob the torch, literally, and tells him that he must protect The Source now.

Jacob asks what's in the tunnel and Mother says that it's life, death and rebirth, the heart of the island. She tells him to never go down there because what will happen would be much worse than death.

Mother then pulls out the bottle of wine (the same one from "Ab Aeterno") and a cup. She chants in Latin was has been deciphered as "Nam non accipimus hoc quasi vulgarem potionem, sed ut ille sit quasi unus mecum." That roughly means "For we do not accept this just as a common drink, but as if that (he?) should be one with me."

She pours some wine into the cup and tells Jacob to Drink. She says that if he drinks, he accepts the responsibility of protecting the island as long as he can, and then he'll have to find his replacement. Jacob says that he doesn't want to protect the island. She says that someone has to and Jacob says that he doesn't care. She says that her time is over and it has to be Jacob that takes over.

Jacob gets emotional and says that he doesn't have to be him because she wanted it to be MIB, and now "I’m all you have." Mother says that it was always supposed to be Jacob and she sees that now and one day he will too. She adds that the doesn't really have a choice though, so he must take the cup and drink.

Jacob reluctantly takes the cup and drinks. Mother then takes his hand and says "Now, you and I... are the same."

So we see that Mother essentially forces Jacob to take the role of protector of the island. She says that he doesn't have a choice, which likely led to Jacob's view that everything is a choice, which he told Hurley in the back of the cab in "The Incident." Jacob has always seemed to push people in a certain direction, but never forces them to do anything. Jacob seems to do many things differently as the protector of the island.

Man in black is given wine by Jacob, smashes the bottle

In one last flashback, we see the man in black sitting on a hill overlooking the valley. Jacob approaches and sees the man passing the white stone from hand to hand. Jacob points it out and the man tells him not to gloat. The stone signifies Richard's choosing Jacob's side.

Jacob then rhetorically asks if he tried to kill him and the man says that he just wants to leave and asks Jacob to let him in a begging tone. Jacob says that as long as he's alive, the man isn't going to leave and adds that even if he manages to kill him, someone else would just take his place. The man says that he would kill the replacements too.

Jacob pulls out the bottle of wine he shared with Richard earlier and gives to the man to help him pass the time. Once Jacob says "I'll see you around" and then leaves. The man says "sooner than you think" and smashes the bottle on the log.

So, if the island is the cork, what does breaking the glass mean? It also seems, at least by Jacob's tone, that this is the first time the man in black has tried to kill Jacob. If people have come and gone (meaning died) many times before, why has the man waited until now to try to get rid of Jacob?

Jacob explains that the island is a cork to contain evil, gives Richard eternal life

Richard sits outside the statue wrapped in a blanket as Jacob approaches carrying a bottle of wine. Richard asks what is inside the statue and Jacob only says that no one comes in unless he invites them in. Jacob tells Richard that he is not the devil and reveals that he brought the Black Rock to the island.

Jacob then tells Richard to think of the wine in the bottle as hell or malevolence, evil or darkness. He says that if the evil got out, it would spread and that the cork in the bottle is the island, which keeps the evil where it belongs.

He continues explaining that the man in black believes that everyone is corruptible because it is in their nature to sin. Jacob says he brings people here to the island prove him wrong, because on the island, their past doesn't matter.

He said that before Richard, there were many other people who all died. Jacob says that he didn't help the people because he wanted them to help themselves and to make the decision between right and wrong for themselves. When Richard points out that if Jacob doesn't step in, the man in black will, this intrigues Jacob, who then offers Richard a job as his intermediary. Richard would be the the one to interact with the people Jacob brings to the island.

Richard asks what he'll get in return for doing the job. He first asks for Isabella back and Jacob says he can't do that. Then Richard asks for his sins to be absolved so he won't go to hell, but Jacob says the can't do that either. Finally, Richard says that he never wants to die, he wants to live forever. Jacob says he can do that, and touches Richard on the shoulder.

So this scene was possibly the biggest mythological reveal to date. We get an explanation of the island's possible purpose from someone who would actually know. The question is, what happens when the cork is not in the bottle and the evil escapes? What consequences would there be? And how does the island act as said cork? What force is it that keeps the evil on the island?

We also see the moment where Richard became the ageless go-between we've come to know. It's surprising that he asked to live forever rather than Jacob giving him the gift on his own.