This isn't really clear yet. We have established that he now wants to protect the leaf village, because Itachi and his wish. Personally I think he is just looking for a motivator.
His entire life was about killing Itachi, it was all he lived for. But when Itachi died he had to find something else to live for - destroying Konoha. But now that he can't do that, he needs something else, or he has nothing to live for. And we already know that going back to Konoha isn't going to be easy for him, not now that he's a missing-nin. So all we can assume for now is that he is doing it to give himself a reason to return and a reason to keep living.