2 This then being the first refutation, the next after it is that which relates to the disciples. For not always in one way only, but also in a second and third, He solves their objections, being minded most abundantly to silence their shamelessness. Which sort of thing He did also with respect to the Sabbath, bringing forward David, the priests, the testimony that says, “I will have mercy, and not sacrifice,” the cause of the Sabbath, for which it was ordained; “for the Sabbath,” says He, was for man. This then He does in the present case also: where after the first He proceeds to a second refutation, plainer than the former.
“For if I,” says He, “by Beelzebub cast out devils, by whom do your sons cast them out?”
See here too His gentleness. For He said not, “my disciples,” nor, “the apostles,” but “your sons;” to the end that if indeed they were minded to return to the same nobleness with them, they might derive hence a powerful spring that way; but if they were uncandid, and continued in the same course, they might not thenceforth be able to allege any plea, though ever so shameless.
But what He says is like this, “By whom do the apostles cast them out?” For in fact they were doing so already, because they had received authority from Him, and these men brought no charge against them; their quarrel not being with the acts, but with the person only. As then it was His will to show that their sayings arose only from their envy against Him, He brings forward the apostles; thus: If I so cast them out, much more those, who have received their authority from me. Nevertheless, no such thing have ye said to them. How then bring ye these charges against me, the author of their doings, while acquitting them of the accusations? This, however, will not free you from your punishment, rather it will condemn you the more. Therefore also He added, “They shall be your judges.” For when persons from among you, and having been practised in these things, both believe me and obey, it is most clear that they will also condemn those who are against me both in deed and word.
“But if I cast out devils by the Spirit of God, then the Kingdom of God has come unto you.”
What means “the Kingdom”? “My coming.” See how again He conciliates and soothes them, and draws them to the knowledge of Himself, and signifies that they are warring with their own good, and contentious against their own salvation. “For whereas ye ought to rejoice,” says He, “and leap for joy, that One has come bestowing those great and unutterable blessings, hymned of old by the prophets, and that the time of your prosperity is at hand; ye do the contrary; so far from receiving the blessings, you do even speak ill of them, and frame accusations that have no real being.”
Now Matthew indeed says, “If I by the Spirit of God cast out”; but Luke, “If I by the finger of God cast out the devils:” implying that to cast out devils is a work of the greatest power, and not of any ordinary grace. And He means indeed that from these things they should infer and say, If this be so, then the Son of God has come. This, however, He says not, but in a reserved way, and so as not to be galling to them, He darkly intimates it by saying, “Then the kingdom of God has come unto you.”
Do you see exceeding wisdom? By the very things which they were blaming, He showed His presence shining forth.
Then, to conciliate them, He said not simply, “The Kingdom has come,” but, “unto you,” as though He had said, To you the good things have come; wherefore then feel displeased at your proper blessings? Why war against your own salvation? This is that time, which the prophets long ago foretold: this, the sign of that advent which was celebrated by them, even these things being wrought by divine power. For the fact indeed, that they are wrought, yourselves know; but that they are wrought by divine power, the deeds themselves cry out. Yea, and it is impossible that Satan should be stronger now; rather he must of absolute necessity be weak. But it cannot be, that he who is weak should, as though he were strong, cast out the strong devil.
Now thus speaking He signified the power of charity, and the weakness of separation and contentiousness. Wherefore He was Himself also continually charging His disciples, on every occasion, concerning charity, and teaching them that the devil, to subvert it, leaves nothing undone.
Source: Homilies on the Gospel of St. Matthew (New Advent)