I also believe it was a personal warning. I also believe it was a warning or a statement to Hurley for them all. So far the castaways have delt with many personal issues between themselves.(in SE1) Ethan, Desmond and Rouseau are the only people outside of their group they have delt with. Of course they have the "monster" to deal with, too. The Tailenders, though, they have delt with a more dangerous and extremely violent element, I'm guessing the "others".(or one group of others) They all carry hand made weapons, do not trust anyone outside of thier group, and HAD 23 survivors. I believe this violent element (others) is coming to the castaways. I think everythings going to change for that reason. At the same time Jin was in Hurleys dream, Jin is finding out about the tailenders and the "others" and how unlucky they have been compared to his own group.
That is my take on it anyway...