Well, I thought it was pretty obvious. Sting is in some ways the Undertaker of TNA. He's the most senior member of the roster (or was), he's been wrestling longer than some of them have been alive etc and he's respected by all. He is allowed to disappear and return at will and the fans will ALWAYS pop for him.
Sting is watching his company change and though Hogan is a bigger name, Sting is in many ways TNA's godfather. By putting him in camera witnessing what's taking place it's putting the idea in viewers' minds "oooh what will Sting make of all this?"
In many ways he fits into it by making people ask where he fits into it. He's the lone enigma with Hogan playing King of the Faces, Jarrett and Foley somehow being made heels due to Hogan being a face, Flair & AJ are heels, the Band are heels, Angle and Joe are faces, Nash may well have turned face. The one man left to choose a side is Sting. Will he side with his mentor and best opponent Ric Flair and pupil AJ Styles against a man he used to despise Hulk Hogan, or will he side with Jarrett and the company he's been the big dog in for nearly 5 years and show his distaste for what Flair is teaching AJ.
I personally think we're building to AJ & Flair vs Kurt & Sting and later Sting vs Flair, perhaps even at Bound for Glory if they can resist putting it on earlier. Sting talked AJ out of retiring, coached him to a world title, "gave" him the win, and was in many ways the true test of AJ's title reign. Flair marched in and corrupted him and it goes against all of Sting's work so he'll be pissed and we'll get that money match twenty years after their first meeting.