If he decides to come back and be a man, among men, then he needs to be assured protection.
He has the keys, he is guilty of treason but if he decides to come back Araknacide is a real problem.
To get Snowden to do what he did, required a massive amount of support and assistance.
He was probably assured that he was being a patriotic actor and his actions were for the best of the 'state'.
Q is telling him the game is up, he has a chance to repent and be judged by an American court rather than a Russian firing squad.