Jacob throws MIB into The Source/The Light, turns MIB into smoke monster

After pummeling the Man In Black at the caves after he killed Mother, Jacob drags MIB through the jungle towards The Source (the tunnel of light/the heart of the island). MIB pleads with Jacob asking him not kill him and explains that she burned his people. Jacob says that he's not going to kill him.

They reach the stream leading to the light and Jacob tosses MIB into the shallow water. MIB looks up at the light and says "She brought you back here?" Jacob says yes because he is now responsible for protecting it. He picks MIB up by the neck and says "You want to find the light? You want to leave this place, brother? Then go."

Jacob then throws MIB into the deeper water and MIB hits his head slams into a rock before floating into the light. Jacob watches as MIB floats into the tunnel and then goes over the edge of the waterfall. Moments later, the ground starts rumbling, the the tunnel gets a little darker and hazy and the tell-tale sounds of the smoke monster can be heard.

The smoke monster comes storming out of the tunnel, knocking Jacob backwards. Jacob stares up in awe as the monster quickly disappears into the jungle.

So this is the origin of the smoke monster. Jacob is the cause of it, and if he hadn't thrown MIB into The Source, a lot of pain and misery for many people could have possibly been avoided. In other words, Jacob's trying to punish MIB for killing mother, ended up making him the powerful creature that he is.

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.

Mother takes Jacob & MIB to the cave of light, the manifestation of life, death & rebirth

As Mother tends to her garden, Jacob and the Man In Black run back to tell her about the men they saw who killed a boar. Jacob asked her where they came from and says they look like them. She says that they're not like them and they don't belong there because she and boys are there for a reason. MIB asks her what the reason is that they are there, and she says it's not time, but he repeats his question more emphatically.

Not long later, we see Mother leading the boys who are blindfolded through the jungle. MIB asks her if she knew about the people, and she says yes. He asks why she didn't tell them about the people and she says because they are dangerous and she didn't want to frighten the boys. When Jacob asks what makes them dangerous she says "the same thing that makes all men dangerous" Then we hear her repeat MIB's line from "The Incident," which is "They come, they fight, they destroy, they corrupt... and it always ends the same."

When MIB then asks where the people came from, she lies and says from another part of the island. She says that they can never go looking for them because if they found them, the people would hurt them. We Jacob asks why the would hurt them, Mother says that it's because they are human and that's what they do.

MIB says that they are people too, and asks if that means they can hurt each other. Mother removes their blindfolds and tells them that she has made it so they can never hurt each other.

Mother turns the boys around where they can see a stream of water flowing into a tunnel with a bright, glowing, yellow light. She tells them that this is the reason they are here. As the boys approach the tunnel, she tells them not to go in.

She says that the light inside is the warmest, brightest light they've ever seen or felt and they must make sure that no one ever finds it. She says that there is a little bit of this light inside of every man, but they always want more. She says that no one could take it, but if someone tried to, they could put it out. She adds if the light goes out there, that it goes out everywhere. She says that she has protected this place, but she can't do it forever, and one day, either Jacob or MIB will have to do it.

Whew. That was a heavy scene. So we a general idea of what is being protected on the island and that it can be accessed from this secret location. This poses a lot of questions that there is not time to answer, but has any unauthorized person every accessed this location during their time on the island? What will happen if this light goes out? Something tells me that this location may have something to do with why Desmond was brought back to the island.