Catena Aurea on Mark 9:14–29: Jerome

Again, the Lord applies to the evil spirit what he had inflicted on the man, calling him a “deaf and dumb spirit,” because he never will hear and speak what the penitent sinner can speak and hear. But the devil, quitting a man, never returns, if the man keep his heart with the keys of humility and charity, and hold possession of the gate of freedom [ed. note: of “fastness”.]. The man who was healed became as one dead, for it is said to those who are healed, “Ye are dead, and your life is hid with Christ in God.”