Mark 5:13

(Vict. Ant. e Cat. in Marc.) He wished to show publicly the fury which devils entertain against men, and that they would inflict much worse things upon men, if they were not hindered by Divine power; because, again, His compassion would not allow this to be shown on men, He permitted them to enter into the swine, that on them the fury and power of the devils might be made known. There follows: And the unclean spirits went out.

(ubi sup.) And He gave them leave, that by the killing of the swine, the salvation of men might be furthered.

Or by this it is signified that devils enter into those men, who live like swine, rolling themselves in the slough of pleasure; they drive them headlong into the sea down the precipice of perdition, into the sea of an evil life where they are choked.

The devils entered not into the swine of their own will, but their asking for this concession, was, that it might be shown that they cannot hurt men without Divine permission. They did not ask to be sent into men, because they saw that He, by whose power they were tortured, bore a human form. Nor did they desire to be sent into the flocks, for they are clean animals offered up in the temple of God. But they desired to be sent into the swine, because no animal is more unclean than a hog, and devils always delight in filthiness. It goes on: And forthwith Jesus gave them leave.

(ubi sup.) Who dwelt in the tombs, because they delighted in dead works, that is, in sins; who were ever raging night and day, because whether in prosperity or in adversity, they were never free from the service of malignant spirits: again, by the foulness of their works, they lay as it were in the tombs, in their lofty pride, they wandered over the mountains, by words of most hardened infidelity, they as it were cut themselves with stones. But he said, My name is Legion, because the Gentile people were enslaved to divers idolatrous forms of worship. Again, that the unclean spirits going out from man enter into swine, which they cast headlong into the sea, implies that now that the people of the Gentiles are freed from the empire of demons, they who have not chosen to believe in Christ, work sacrilegious rites in hidden places.