Matthew 8:31

The dæmons seeing that there is no longer any place left for them among the Gentiles, pray that they may be suffered to dwell among the heretics; these, seized by them, are drowned in the sea, that is, in worldly desires, by the instigations of the dæmons, and perish in the unbelief of the rest of the Gentiles.

They did not ask to be sent into men, because they saw Him by whose excellence they were tortured existing in human shape. Nor did they ask to be sent into sheep, because sheep are by God's institution clean animals, and were then offered in the temple of God. But they requested to be sent into the swine rather than into any of the other unclean animals, because this is of all animals the most unclean; whence also it has its name 'porcus,' as being 'spurcus,' filthy, and delighting in filthiness; and dæmons also delight in the filthiness of sin. They did not pray that they might be sent into the air, because of their eager desire of hurting men. And he saith unto them, Go.

(Mor. ii. 10.) For the Devil knows that of himself he has no power to do any thing, because it is not of himself that he exists as a spirit.

Now, should any one say, "And wherefore did Christ fulfill the devils' request, suffering them to depart into the herd of swine?" this would be our reply, that He did so, not as yielding to them, but as providing for many objects thereby. One, to teach them that are delivered from those wicked tyrants, how great the malice of their insidious enemies; another, that all might learn, how not even against swine are they bold, except He allow them; a third, that they would have treated those men more grievously than the swine, unless even in their calamity they had enjoyed much of God's providential care. For that they hate us more than the brutes is surely evident to every man. So then they that spared not the swine, but in one moment of time cast them all down the precipice, much more would they have done so to the men whom they possessed, leading them towards the desert, and carrying them away, unless even in their very tyranny the guardian care of God had abounded, to curb and check the excess of their violence. Whence it is manifest that there is no one, who doth not enjoy the benefit of God's providence. And if not all alike, nor after one manner, this is itself a very great instance of providence; in that according to each man's profit, the work also of providence is displayed. And besides what hath been mentioned, there is another thing also, which we learn from this; that His providence is not only over all in common, but also over each in particular; which He also declared with respect to His disciples, saying, "But the very hairs of your head are numbered." And from these demoniacs too, one may clearly perceive this; who would have been choked long before, if they had not enjoyed the benefit of much tender care from above.

(De. Cons. Ev. ii. 24.) Though the words of the daemons are variously reported by the three Evangelists, yet this is no difficulty; for they either all convey the same sense, or may be supposed to have been all spoken. Nor again because in Matthew they speak in the plural, in the others in the singular number; because even the other two Evangelists relate that when asked his name, he answered, Legion, showing that the daemons were many. Now there was not far from thence a herd of many swine feeding; and the daemons prayed him, saying, If thou cast us out hence, send us into the swine.