His response here makes it clear that his authority is key: “…the Son of Man has authority on earth to forgive sins…” At this point, the sins of the paralytic have been forgiven, the question is one of authority by witnesses of the event. They didn’t ask “if” he could do it, but by what authority was he doing it. It was not enough to be there with him, in his house, to witness the sins being forgiven, these were the scribes, the most intelligent of the Jews, and they were obviously a little slow.
They ask, how could anyone who was not God, meaning Jahweh, forgive sins? Jesus demonstrates his Imperial authority by which he can pardon anyone. In response to their patent disbelief, Jesus orders the paralytic to walk out of the room to demonstrate that his authority is absolute. Before he does so, he suggests that for one with sufficient authority, forgiving sins and healing a paralyzed person is equally simple. How miraculous this is depends on how one interprets the term ‘paralytic’.