Desmond, Jacob and Wallace by jumbotron007

I am sorry if this has been posted already but this has been in my mind for long.

Why is Desmond on the island? Whats his link to Jacob?

I think due to the time traveling antics of the losties, a tangential universe the FST was created which was not anticipated by Jacob.

Jacob was not with the idea of Widmore finding the island. Remember Bram and others trying to prevent Miles from going to the island. They were trying their best to thwart Widmore finding the island. I think Jacob only likes it when he brings people to the island. When they find the island on their own it does not go well with him. I think he chooses whom to bring based on their lives in the lighthouse. The military, the Dharma initiative came on their own. I think Jacob ordered the purge since the Dharma were messing with the island.We all now know that Richard takes orders from Jacob only and was not messed up in that like Ben. I still think the purge was carried out in Richard's leadership not widmore or Ben. In the purge scene we can see that its Richard who comes out and looks at his watch and takes off his mask and others follow suit. At least that is enough evidence to convince me that he is in command of the operation.One more conclusive proof that Jacob ordered so! me killings is in 1954 in "Jughead" when Richard says "Whatever your, uh, your superiors told you, I want you to know the truth. A month ago, we found 18 members of an Army battalion right here in our jungle here, setting up this camp. We gave them the opportunity to leave the island peacefully. They weren't willing to do that, so I was forced to kill 'em. All of 'em. " and goes on to say
"Y--you answer to someone, don't you? You follow a chain of command, right? "
So from this we can go on to extrapolate that Jacob found out that Widmore found the island he tried to prevent it at all costs(Bram kidnapping Miles,Tom planting Michael in the boat etc) and it is not MIB who told as Christian to move the island but Jacob or someone else impersonating Christian(I think there is a 3rd player).Think about it. MIB cares a damn about the island and he would not want to protect it now.At this point he wants is to leave.( its a damn island) Moreover he would not be afraid of a mere few mercenaries when all he has to do is turn into smoke and bang them together against their heads. In fact he would want more people to come and he can use them all to escape.
So I think Widmore's finding the island was not a expected by Jacob or MIB. I simply think MIB simply improvised.

Whatever the case may be, Jacob realised his life was in danger midway when the kahana came and some losties escaped and the donkey wheel was moved and FST was created. And he has to do something in order to course correct else the tangential(unstable) universe will take down the original timeline also with it. He somehow arranged a truce with Widmore to prevent MIb from escaping and also to collapse the FST in excahnge for making him the leader or something. I also think thats what he meant when he said " they are coming" and also Wallace is Desmond(We really don't know anything about his past, do we? We so far don't know the backstories of only 3 people, Desmond, MIb and Jacob. Almost everyone else is shown as a kid.) I think the only way to destroy the FST is by sinking the island. Once the island sinks in FST both the time lines will bleed over and merge as one.I dont think Jacob wants to kill MIb by sinking the island in the original timeline.All he wants to do it prev! ent MIB from escaping and appoint a new Jacob. He loves the island more than anything to destroy it. So here is where our Desmond's special powers come in. He is the 'package' to be transported to the the FST to destroy the island.I am not sure how he is going to do that. We can see there is a time difference between the FST and the OT. Its around 2004 in FST and 2007 in OT.SO i think somehow Desmond will be packaged and transported (figuratively of course) to the FST in the past(i.e. before the losties boarded the Oceanic). Or he will meet Faraday in FST and give him information about time travel from who will tranport them to the past and sink the island. I think would sink the island, flash back to 2004 in Sydney and board the plane 815.