Preaching on a similar episode, St Peter Chyrsologus offers an striking illustration--striking because it is so comforting--concerning the healing that Our Lord graciously bestows. For the miracle is not that Our Lord is capable of healing, but that He wills do to so. And the miracle is that His healing is good for both body and soul. Yet who would think--except one of the sainted fathers--that Our Lord's mercy also produces mourning?
Here is how St Peter Chrysologus puts it:
This one, therefore, was deaf and mute who was not able to hear the Law nor to confess God, but was being tossed about in the fire of Gehenna and through the waters of the ever bitter abyss (Mk 9.22), and was unable to be healed by the disciples or by any other human being, since Christ was at that time called the Hearing of faith (Rom 10.17), the Confession of salvation (Rom 10.10), the Redemption and Life of the gentiles.
In short, when the devil was put to flight by Christ's command, what had been shut is opened, bonds are loosed, speech is given back, hearing returns, the man is restored, and only the devil is in mourning that he has been forced out of the one he had possessed for so long. This is why the one who comes from paganism is first cleansed of the demon by the imposition of hands in exorcism and then receives the opening of his ears, so that he can acquire a hearing of faith, so that he can attain to salvation with the Lord accompanying him.