Matthew 12:45

When there is forgiveness of sins through the sacraments, the house is cleaned; but the Holy Spirit must be a necessary inhabitant. And the Holy Spirit inhabits only those who are humble of heart, for God says, "Upon whom will my Spirit rest?" And he answers the question: "Upon the one who is humble and quiet and who fears my word." Therefore, when he is the inhabitant, he fills up, rules, acts, deters from evil, inspires one to do good and tempers justice with sweetness, so that one may do good with the love of an upright heart and not with the fear of punishment. But once that unclean spirit that made you evil has gone out of you, that is, from your mind, when your sins have been forgiven, it roams through dry places in search of a resting place. Finding none, the unclean spirit returns to his house, where he finds everything clean and in order. Then he takes with him seven other spirits more evil than himself; and the last state of that person becomes worse than the first. He takes with him seven other spirits. What is meant by "seven other spirits"? Is the unclean spirit itself sevenfold? What does this mean? By seven the whole group is signified. The whole spirit went away, the whole spirit came back; and would that only one spirit returned! What does it mean: "He takes with him seven other spirits"? Those spirits you did not have when you were evil, you will have unexpectedly when you are good. Listen carefully while I explain as best I can. […]

(Quæst. Ev. i. 8.) So that in these words the Lord signifies that some shall so believe, as not to have strength for the work of continence, and shall return to the world. He taketh unto him other seven, is to be understood that when any has fallen from righteousness, he shall also have hypocrisy. For the lust of the flesh being cast out of its wonted works by penitence, when it finds not any delights in which it may rest, returns the more greedily, and again takes possession of the soul, if carelessness has ensued, and there has not been introduced as the dweller in the cleansed abode the word of God in sound doctrine. And as he will not only have the seven vices which are the contraries of the spiritual virtues, but will hypocritically feign that he has the virtues, therefore his old lust, taking to itself seven other worse, that is, this seven-fold hypocrisy, returns to him so as to make the last state of that man worse than the former.

This is said with good reason. For when someone who has once been freed from evils loses self-control, he suffers a much worse fall than previously. For this reason "he passes through waterless places seeking rest." This indicates how thoroughly the demons' stratagem has taken hold of such a person—completely and absolutely. There are many reasons why such a person should have kept himself under control before it is too late. He has already suffered. He has been redeemed. The threat of a worse future punishment should be constraining. But none of these reasons has prevailed to make them better.Now remember how the evil spirit inhabited the people when they were in Egypt, how they lived according to Egyptian customs and laws and became filled with all kinds of uncleanness. When they had been delivered by Moses and had received the law as a guide calling them to the light of true divine knowledge, the wicked and unclean spirit left them. But what happens when someone who has believed now disbelieves? The demons again take up their abode there with a vengeance. For just as the Holy Spirit, when he sees a person's heart desisting from all uncleanness, abides and dwells and rests in that one, so also the unclean spirit likes to take lodging in the souls of the lawless.

When therefore He had condemned them, having proved most amply that they were sinning inexcusably, and that their disobedience arose from their own perverseness not from their Teacher's inability, and when He had demonstrated this as well by many other arguments, as also by the Ninevites, and by the queen: then He speaks also of the punishment that should overtake them, darkly indeed, yet He doth speak of it, interweaving an intense fear in His narration. "For when," saith He, "the unclean spirit is gone out of the man, he walketh through dry places, seeking rest; and finding none, he saith, I will return to my house from whence I came out; and when he is come, he findeth it empty, and swept and garnished. Then goeth he, and taketh with himself seven other spirits more wicked than himself, and they enter in and dwell there, and the last state of that man is worse than the first. Even so shall it be also unto this generation." By this He signifies, that not only in the world to come, but here too they should suffer most grievously. For since He had said, "The men of Nineveh shall rise up in judgment, and shall condemn this generation;" lest, on account of the postponement of the time, they should despise and grow more careless, by this He brings His terror close upon them. Wherewith the prophet Hosea likewise threatening them said, that they should be "even as the prophet that is beside himself, the man that is carried away by a spirit;" that is to say, as the madmen, and distracted by evil spirits, even the false prophets. For here, by "a prophet that is beside himself," he means the false prophet, such as are the augurs. […]

Some suppose that this place is spoken of heretics, because the unclean spirit who dwelt in them before when they were Gentiles, is cast out before the confession of the true faith; when after they went over to heresy, and garnished their house with feigned virtues, then it is that the Devil, having taken to him other seven evil spirits, returns and dwells in them; and their last state becomes worse than their first. And indeed heretics are in a much worse condition than the Gentiles; for in the heretics was a hope of faith, in the Gentiles a war of discord. Yet though this exposition has a plausibility and a show of learning, I am doubtful of its truth. For by the concluding words of this, whether it be parable or example, Titus shall it he to this evil generation, we are compelled to refer it, not to heretics, or to men in general, but to the Jewish people. So the context of the passage may not shift about loosely and vaguely, and be like unmeaning speeches, but may be consistent with itself from first to last. The unclean spirit then went out from the Jews when they received the Law; and being cast out of the Jews, he walked through the wilderness of the Gentiles; as it follows, He walketh through dry places seeking rest. And when they believed on the Lord, the Devil, finding no place among the nations, said, I will return into my house whence I came out; I have the Jews from whom I formerly departed. And when he is come, he findeth it empty, swept, and garnished. For the temple of the Jews was empty, and had not Christ to dwell therein, He having said, Arise, let us go hence. (John 14:31) Seeing then they had not the protection of Angels, and were burdened with the useless observances of the Law, and the traditions of the Pharisees, the Devil returns to his former dwelling, and, taking to him seven other dæmons, inhabits it as before. […]