Translation
Or how is it possible for someone to enter into the house of a strong man and take away the vessels containing his goods if he does not first tie up the strong man? Then he can rob his house.
Paraphrase
How then is it possible that I have entered Satan’s realm (the physical world) and I am succeeding at capturing that which he thought he possessed securely (people’s allegiance), unless it is true that I have also rendered him powerless? That is the reason I can take what he thought was his alone.