Calling Kafir
To call someone kafir is not your jurisdiction. It is just like punishing a thief. You cannot punish him but the court can. In this matter of calling someone kafir the authority is God only. Our justification is to tell that his or her idea or belief or argument is wrong. Having said that, if a person denies Qur’an for his claim, he is admitting he is kafir, this is a contradiction denying Qur’an and claiming Muslim. but if he adopts an interpretation that he meant that God speaks through a person or saint or he manifest the spirit of God, and he doesn’t deny the fact that there is only one God, now this in interpretation, which we call wrong but whether or not he is actually denying or making fasle excuses, this is between him and his God. Only He can tell him his reality.