I'm a bit confused about what you're asking but...
-Sora isn't considered special. He's an all around average kid who doesn't do anything that anyone else couldn't. The only thing that sets him apart is that he does do what others aren't willing to do, like open his heart to anyone and retain a childlike wonder even though he's not a small child anymore.
-Xehanort wants him as a vessel, but again, this is nothing special. He just needs one last person and with a narrowing pool of people, Sora seemed like a good choice. Riku failed because he built a resistance to the darkness, Roxas failed because he was too self aware, so Sora was left as the most vulnerable. His naivety and cockiness made him an easy target.
-Light can't be destroyed. Xehanort just wants to reach Kingdom Hearts for a number of reasons, but none of them are to destroy light.