Summa Th. I-II EN Qu.77 a.8
Objection: 1. It would seem that sin committed through passion cannot be mortal. Because venial sin is condivided with mortal sin. Now sin committed from weakness is venial, since it has in itself a motive for pardon [venia]. Since therefore sin committed through passion is a sin of weakness, it seems that it cannot be mortal.
2. Further, the cause is more powerful than its effect. But passion cannot be a mortal sin, for there is no mortal sin in the sensuality, as stated above (Question , Article ). Therefore a sin committed through passion cannot be mortal.
3. Further, passion is a hindrance to reason, as explained above (Articles ,2). Now it belongs to the reason to turn to God, or to turn away from Him, which is the essence of a mortal sin. Therefore a sin committed through passion cannot be mortal.
On the contrary The Apostle says (Rm 7,5) that "the passions of the sins . . . work [Vulg.: 'did work'] in our members to bring forth fruit unto death." Now it is proper to mortal sin to bring forth fruit unto death. Therefore sin committed through passion may be mortal.
I answer that Mortal sin, as stated above (Question , Article ), consists in turning away from our last end which is God, which aversion pertains to the deliberating reason, whose function it is also to direct towards the end. Therefore that which is contrary to the last end can happen not to be a mortal sin, only when the deliberating reason is unable to come to the rescue, which is the case in sudden movements. Now when anyone proceeds from passion to a sinful act, or to a deliberate consent, this does not happen suddenly: and so the deliberating reason can come to the rescue here, since it can drive the passion away, or at least prevent it from having its effect, as stated above: wherefore if it does not come to the rescue, there is a mortal sin; and it is thus, as we see, that many murders and adulteries are committed through passion.
Reply to Objection: 1. A sin may be venial in three ways. First, through its cause, i.e. through having cause to be forgiven, which cause lessens the sin; thus a sin that is committed through weakness or ignorance is said to be venial. Secondly, through its issue; thus every sin, through repentance, becomes venial, i.e. receives pardon [veniam]. Thirdly, by its genus, e.g. an idle word. This is the only kind of venial sin that is opposed to mortal sin: whereas the objection regards the first kind.
2. Passion causes sin as regards the adherence to something. But that this be a mortal sin regards the aversion, which follows accidentally from the adherence, as stated above (Article , ad 1): hence the argument does not prove.
3. Passion does not always hinder the act of reason altogether: consequently the reason remains in possession of its free-will, so as to turn away from God, or turn to Him. If, however, the use of reason be taken away altogether, the sin is no longer either mortal or venial.
We must now consider the cause of sin on the part of the will, viz. malice: and under this head there are four points of inquiry:
(1) Whether it is possible for anyone to sin through certain malice, i.e. purposely?
(2) Whether everyone that sins through habit, sins through certain malice?
(3) Whether every one that sins through certain malice, sins through habit?
(4) Whether it is more grievous to sin through certain malice, than through passion?
Objection: 1. It would seem that no one sins purposely, or through certain malice. Because ignorance is opposed to purpose or certain malice. Now "every evil man is ignorant," according to the Philosopher (Ethic. iii, 1); and it is written (Pr 14,22): "They err that work evil." Therefore no one sins through certain malice.
2. Further, Dionysius says (Div. Nom. iv) that "no one works intending evil." Now to sin through malice seems to denote the intention of doing evil [*Alluding to the derivation of "malitia" (malice) from "malum" (evil)] in sinning, because an act is not denominated from that which is unintentional and accidental. Therefore no one sins through malice.
3. Further, malice itself is a sin. If therefore malice is a cause of sin, it follows that sin goes on causing sin indefinitely, which is absurd. Therefore no one sins through malice.
On the contrary It is written (Jb 34,27): "[Who] as it were on purpose have revolted from God [Vulg.: 'Him'], and would not understand all His ways." Now to revolt from God is to sin. Therefore some sin purposely or through certain malice.
I answer that Man like any other being has naturally an appetite for the good; and so if his appetite incline away to evil, this is due to corruption or disorder in some one of the principles of man: for it is thus that sin occurs in the actions of natural things. Now the principles of human acts are the intellect, and the appetite, both rational (i.e. the will) and sensitive. Therefore even as sin occurs in human acts, sometimes through a defect of the intellect, as when anyone sins through ignorance, and sometimes through a defect in the sensitive appetite, as when anyone sins through passion, so too does it occur through a defect consisting in a disorder of the will. Now the will is out of order when it loves more the lesser good. Again, the consequence of loving a thing less is that one chooses to suffer some hurt in its regard, in order to obtain a good that one loves more: as when a man, even knowingly, suffers the loss of a limb, that he may save his life which he loves more. Accordingly when an inordinate will loves some temporal good, e.g. riches or pleasure, more than the order of reason or Divine law, or Divine charity, or some such thing, it follows that it is willing to suffer the loss of some spiritual good, so that it may obtain possession of some temporal good. Now evil is merely the privation of some good; and so a man wishes knowingly a spiritual evil, which is evil simply, whereby he is deprived of a spiritual good, in order to possess a temporal good: wherefore he is said to sin through certain malice or on purpose, because he chooses evil knowingly.
Reply to Objection: 1. Ignorance sometimes excludes the simple knowledge that a particular action is evil, and then man is said to sin through ignorance: sometimes it excludes the knowledge that a particular action is evil at this particular moment, as when he sins through passion: and sometimes it excludes the knowledge that a particular evil is not to be suffered for the sake of possessing a particular good, but not the simple knowledge that it is an evil: it is thus that a man is ignorant, when he sins through certain malice.
2. Evil cannot be intended by anyone for its own sake; but it can be intended for the sake of avoiding another evil, or obtaining another good, as stated above: and in this case anyone would choose to obtain a good intended for its own sake, without suffering loss of the other good; even as a lustful man would wish to enjoy a pleasure without offending God; but with the two set before him to choose from, he prefers sinning and thereby incurring God's anger, to being deprived of the pleasure.
3. The malice through which anyone sins, may be taken to denote habitual malice, in the sense in which the Philosopher (Ethic. v, 1) calls an evil habit by the name of malice, just as a good habit is called virtue: and in this way anyone is said to sin through malice when he sins through the inclination of a habit. It may also denote actual malice, whether by malice we mean the choice itself of evil (and thus anyone is said to sin through malice, in so far as he sins through making a choice of evil), or whether by malice we mean some previous fault that gives rise to a subsequent fault, as when anyone impugns the grace of his brother through envy. Nor does this imply that a thing is its own cause: for the interior act is the cause of the exterior act, and one sin is the cause of another; not indefinitely, however, since we can trace it back to some previous sin, which is not caused by any previous sin, as was explained above (Question , Article , ad 3).
Objection: 1. It would seem that not every one who sins through habit, sins through certain malice. Because sin committed through certain malice, seems to be most grievous. Now it happens sometimes that a man commits a slight sin through habit, as when he utters an idle word. Therefore sin committed from habit is not always committed through certain malice.
2. Further, "Acts proceeding from habits are like the acts by which those habits were formed" (Ethic. ii, 1,2). But the acts which precede a vicious habit are not committed through certain malice. Therefore the sins that arise from habit are not committed through certain malice.
3. Further, when a man commits a sin through certain malice, he is glad after having done it, according to Pr 2,14: "Who are glad when they have done evil, and rejoice in most wicked things": and this, because it is pleasant to obtain what we desire, and to do those actions which are connatural to us by reason of habit. But those who sin through habit, are sorrowful after committing a sin: because "bad men," i.e. those who have a vicious habit, "are full of remorse" (Ethic. ix, 4). Therefore sins that arise from habit are not committed through certain malice.
On the contrary A sin committed through certain malice is one that is done through choice of evil. Now we make choice of those things to which we are inclined by habit, as stated in Ethic. vi, 2 with regard to virtuous habits. Therefore a sin that arises from habit is committed through certain malice.
I answer that There is a difference between a sin committed by one who has the habit, and a sin committed by habit: for it is not necessary to use a habit, since it is subject to the will of the person who has that habit. Hence habit is defined as being "something we use when we will," as stated above (Question , Article ). And thus, even as it may happen that one who has a vicious habit may break forth into a virtuous act, because a bad habit does not corrupt reason altogether, something of which remains unimpaired, the result being that a sinner does some works which are generically good; so too it may happen sometimes that one who has a vicious habit, acts, not from that habit, but through the uprising of a passion, or again through ignorance. But whenever he uses the vicious habit he must needs sin through certain malice: because to anyone that has a habit, whatever is befitting to him in respect of that habit, has the aspect of something lovable, since it thereby becomes, in a way, connatural to him, according as custom and habit are a second nature. Now the very thing which befits a man in respect of a vicious habit, is something that excludes a spiritual good: the result being that a man chooses a spiritual evil, that he may obtain possession of what befits him in respect of that habit: and this is to sin through certain malice. Wherefore it is evident that whoever sins through habit, sins through certain malice.
Reply to Objection: 1. Venial sin does not exclude spiritual good, consisting in the grace of God or charity. Wherefore it is an evil, not simply, but in a relative sense: and for that reason the habit thereof is not a simple but a relative evil.
2. Acts proceeding from habits are of like species as the acts from which those habits were formed: but they differ from them as perfect from imperfect. Such is the difference between sin committed through certain malice and sin committed through passion.
3. He that sins through habit is always glad for what he does through habit, as long as he uses the habit. But since he is able not to use the habit, and to think of something else, by means of his reason, which is not altogether corrupted, it may happen that while not using the habit he is sorry for what he has done through the habit. And so it often happens that such a man is sorry for his sin not because sin in itself is displeasing to him, but on account of his reaping some disadvantage from the sin.
Objection: 1. It would seem that whoever sins through certain malice, sins through habit. For the Philosopher says (Ethic. v, 9) that "an unjust action is not done as an unjust man does it," i.e. through choice, "unless it be done through habit." Now to sin through certain malice is to sin through making a choice of evil, as stated above (Article ). Therefore no one sins through certain malice, unless he has the habit of sin.
2. Further, Origen says (Peri Archon iii) that "a man is not suddenly ruined and lost, but must needs fall away little by little." But the greatest fall seems to be that of the man who sins through certain malice. Therefore a man comes to sin through certain malice, not from the outset, but from inveterate custom, which may engender a habit.
3. Further, whenever a man sins through certain malice, his will must needs be inclined of itself to the evil he chooses. But by the nature of that power man is inclined, not to evil but to good. Therefore if he chooses evil, this must be due to something supervening, which is passion or habit. Now when a man sins through passion, he sins not through certain malice, but through weakness, as stated (Question , Article ). Therefore whenever anyone sins through certain malice, he sins through habit.
On the contrary The good habit stands in the same relation to the choice of something good, as the bad habit to the choice of something evil. But it happens sometimes that a man, without having the habit of a virtue, chooses that which is good according to that virtue. Therefore sometimes also a man, without having the habit of a vice, may choose evil, which is to sin through certain malice.
I answer that The will is related differently to good and to evil. Because from the very nature of the power, it is inclined to the rational good, as its proper object; wherefore every sin is said to be contrary to nature. Hence, if a will be inclined, by its choice, to some evil, this must be occasioned by something else. Sometimes, in fact, this is occasioned through some defect in the reason, as when anyone sins through ignorance; and sometimes this arises through the impulse of the sensitive appetite, as when anyone sins through passion. Yet neither of these amounts to a sin through certain malice; for then alone does anyone sin through certain malice, when his will is moved to evil of its own accord. This may happen in two ways. First, through his having a corrupt disposition inclining him to evil, so that, in respect of that disposition, some evil is, as it were, suitable and similar to him; and to this thing, by reason of its suitableness, the will tends, as to something good, because everything tends, of its own accord, to that which is suitable to it. Moreover this corrupt disposition is either a habit acquired by custom, or a sickly condition on the part of the body, as in the case of a man who is naturally inclined to certain sins, by reason of some natural corruption in himself. Secondly, the will, of its own accord, may tend to an evil, through the removal of some obstacle: for instance, if a man be prevented from sinning, not through sin being in itself displeasing to him, but through hope of eternal life, or fear of hell, if hope give place to despair, or fear to presumption, he will end in sinning through certain malice, being freed from the bridle, as it were.It is evident, therefore, that sin committed through certain malice, always presupposes some inordinateness in man, which, however, is not always a habit: so that it does not follow of necessity, if a man sins through certain malice, that he sins through habit.
Reply to Objection: 1. To do an action as an unjust man does, may be not only to do unjust things through certain malice, but also to do them with pleasure, and without any notable resistance on the part of reason, and this occurs only in one who has a habit.
2. It is true that a man does not fall suddenly into sin from certain malice, and that something is presupposed; but this something is not always a habit, as stated above.
3. That which inclines the will to evil, is not always a habit or a passion, but at times is something else. Moreover, there is no comparison between choosing good and choosing evil: because evil is never without some good of nature, whereas good can be perfect without the evil of fault.
Objection: 1. It would seem that it is not more grievous to sin through certain malice than through passion. Because ignorance excuses from sin either altogether or in part. Now ignorance is greater in one who sins through certain malice, than in one who sins through passion; since he that sins through certain malice suffers from the worst form of ignorance, which according to the Philosopher (Ethic. vii, 8) is ignorance of principle, for he has a false estimation of the end, which is the principle in matters of action. Therefore there is more excuse for one who sins through certain malice, than for one who sins through passion.
2. Further, the more a man is impelled to sin, the less grievous his sin, as is clear with regard to a man who is thrown headlong into sin by a more impetuous passion. Now he that sins through certain malice, is impelled by habit, the impulse of which is stronger than that of passion. Therefore to sin through habit is less grievous than to sin through passion.
3. Further, to sin through certain malice is to sin through choosing evil. Now he that sins through passion, also chooses evil. Therefore he does not sin less than the man who sins through certain malice.
On the contrary A sin that is committed on purpose, for this very reason deserves heavier punishment, according to Jb 34,26: "He hath struck them as being wicked, in open sight, who, as it were, on purpose, have revolted from Him." Now punishment is not increased except for a graver fault. Therefore a sin is aggravated through being done on purpose, i.e. through certain malice.
I answer that sin committed through malice is more grievous than a sin committed through passion, for three reasons. First, because, as sin consists chiefly in an act of the will, it follows that, other things being equal, a sin is all the more grievous, according as the movement of the sin belongs more to the will. Now when a sin is committed through malice, the movement of sin belongs more to the will, which is then moved to evil of its own accord, than when a sin is committed through passion, when the will is impelled to sin by something extrinsic, as it were. Wherefore a sin is aggravated by the very fact that it is committed through certain malice, and so much the more, as the malice is greater; whereas it is diminished by being committed through passion, and so much the more, as the passion is stronger. Secondly, because the passion which incites the will to sin, soon passes away, so that man repents of his sin, and soon returns to his good intentions; whereas the habit, through which a man sins, is a permanent quality, so that he who sins through malice, abides longer in his sin. For this reason the Philosopher (Ethic. vii, 8) compares the intemperate man, who sins through malice, to a sick man who suffers from a chronic disease, while he compares the incontinent man, who sins through passion, to one who suffers intermittently. Thirdly, because he who sins through certain malice is ill-disposed in respect of the end itself, which is the principle in matters of action; and so the defect is more dangerous than in the case of the man who sins through passion, whose purpose tends to a good end, although this purpose is interrupted on account of the passion, for the time being. Now the worst of all defects is defect of principle. Therefore it is evident that a sin committed through malice is more grievous than one committed through passion.
Reply to Objection: 1. Ignorance of choice, to which the objection refers, neither excuses nor diminishes a sin, as stated above (Question , Article ). Therefore neither does a greater ignorance of the kind make a sin to be less grave.
2. The impulse due to passion, is, as it were, due to a defect which is outside the will: whereas, by a habit, the will is inclined from within. Hence the comparison fails.
3. It is one thing to sin while choosing, and another to sin through choosing. For he that sins through passion, sins while choosing, but not through choosing, because his choosing is not for him the first principle of his sin; for he is induced through the passion, to choose what he would not choose, were it not for the passion. On the other hand, he that sins through certain malice, chooses evil of his own accord, in the way already explained (Articles ,3), so that his choosing, of which he has full control, is the principle of his sin: and for this reason he is said to sin "through" choosing.
We must now consider the external causes of sin, and (1) on the part of God; (2) on the part of the devil; (3) on the part of man.
Under the first head there are four points of inquiry:
(1) Whether God is a cause of sin?
(2) Whether the act of sin is from God?
(3) Whether God is the cause of spiritual blindness and hardness of heart?
(4) Whether these things are directed to the salvation of those who are blinded or hardened?
Objection: 1. It would seem that God is a cause of sin. For the Apostle says of certain ones (Rm 1,28): "God delivered them up to a reprobate sense, to do those things which are not right [Douay: 'convenient']," and a gloss comments on this by saying that "God works in men's hearts, by inclining their wills to whatever He wills, whether to good or to evil." Now sin consists in doing what is not right, and in having a will inclined to evil. Therefore God is to man a cause of sin.
2. Further, it is written (Sg 14,11): "The creatures of God are turned to an abomination; and a temptation to the souls of men." But a temptation usually denotes a provocation to sin. Since therefore creatures were made by God alone, as was established in the I 44,1, it seems that God is a cause of sin, by provoking man to sin.
3. Further, the cause of the cause is the cause of the effect. Now God is the cause of the free-will, which itself is the cause of sin. Therefore God is the cause of sin.
4. Further, every evil is opposed to good. But it is not contrary to God's goodness that He should cause the evil of punishment; since of this evil it is written (Is 45,7) that God creates evil, and (Amos 3:6): "Shall there be evil in the city which God [Vulg.: 'the Lord'] hath not done?" Therefore it is not incompatible with God's goodness that He should cause the evil of fault.
On the contrary It is written (Sg 11,25): "Thou . . . hatest none of the things which Thou hast made." Now God hates sin, according to Sg 14,9: "To God the wicked and his wickedness are hateful." Therefore God is not a cause of sin.
I answer that Man is, in two ways, a cause either of his own or of another's sin. First, directly, namely be inclining his or another's will to sin; secondly, indirectly, namely be not preventing someone from sinning. Hence (Ez 3,18) it is said to the watchman: "If thou say not to the wicked: 'Thou shalt surely die' [*Vulg.: "If, when I say to the wicked, 'Thou shalt surely die,' thou declare it not to him."] . . . I will require his blood at thy hand." Now God cannot be directly the cause of sin, either in Himself or in another, since every sin is a departure from the order which is to God as the end: whereas God inclines and turns all things to Himself as to their last end, as Dionysius states (Div. Nom. i): so that it is impossible that He should be either to Himself or to another the cause of departing from the order which is to Himself. Therefore He cannot be directly the cause of sin. In like manner neither can He cause sin indirectly. For it happens that God does not give some the assistance, whereby they may avoid sin, which assistance were He to give, they would not sin. But He does all this according to the order of His wisdom and justice, since He Himself is Wisdom and Justice: so that if someone sin it is not imputable to Him as though He were the cause of that sin; even as a pilot is not said to cause the wrecking of the ship, through not steering the ship, unless he cease to steer while able and bound to steer. It is therefore evident that God is nowise a cause of sin.
Reply to Objection: 1. As to the words of the Apostle, the solution is clear from the text. For if God delivered some up to a reprobate sense, it follows that they already had a reprobate sense, so as to do what was not right. Accordingly He is said to deliver them up to a reprobate sense, in so far as He does not hinder them from following that reprobate sense, even as we are said to expose a person to danger if we do not protect him. The saying of Augustine (De Grat. et Lib. Arb. xxi, whence the gloss quoted is taken) to the effect that "God inclines men's wills to good and evil," is to be understood as meaning that He inclines the will directly to good; and to evil, in so far as He does not hinder it, as stated above. And yet even this is due as being deserved through a previous sin.
2. When it is said the "creatures of God are turned 'to' an abomination, and a temptation to the souls of men," the preposition "to" does not denote causality but sequel [*This is made clear by the Douay Version: the Latin "factae sunt in abominationem" admits of the translation "were made to be an abomination," which might imply causality.]; for God did not make the creatures that they might be an evil to man; this was the result of man's folly, wherefore the text goes on to say, "and a snare to the feet of the unwise," who, to wit, in their folly, use creatures for a purpose other than that for which they were made.
3. The effect which proceeds from the middle cause, according as it is subordinate to the first cause, is reduced to that first cause; but if it proceed from the middle cause, according as it goes outside the order of the first cause, it is not reduced to that first cause: thus if a servant do anything contrary to his master's orders, it is not ascribed to the master as though he were the cause thereof. In like manner sin, which the free-will commits against the commandment of God, is not attributed to God as being its cause.
4. Punishment is opposed to the good of the person punished, who is thereby deprived of some good or other: but fault is opposed to the good of subordination to God; and so it is directly opposed to the Divine goodness; consequently there is no comparison between fault and punishment.
Objection: 1. It would seem that the act of sin is not from God. For Augustine says (De Perfect. Justit. ii) that "the act of sin is not a thing." Now whatever is from God is a thing. Therefore the act of sin is not from God.
2. Further, man is not said to be the cause of sin, except because he is the cause of the sinful act: for "no one works, intending evil," as Dionysius states (Div. Nom. iv). Now God is not a cause of sin, as stated above (Article ). Therefore God is not the cause of the act of sin.
3. Further, some actions are evil and sinful in their species, as was shown above (Question , Articles ,8). Now whatever is the cause of a thing, causes whatever belongs to it in respect of its species. If therefore God caused the act of sin, He would be the cause of sin, which is false, as was proved above (Article ). Therefore God is not the cause of the act of sin.
On the contrary The act of sin is a movement of the free-will. Now "the will of God is the cause of every movement," as Augustine declares (De Trin. iii, 4,9). Therefore God's will is the cause of the act of sin.
I answer that The act of sin is both a being and an act; and in both respects it is from God. Because every being, whatever the mode of its being, must be derived from the First Being, as Dionysius declares (Div. Nom. v). Again every action is caused by something existing in act, since nothing produces an action save in so far as it is in act; and every being in act is reduced to the First Act, viz. God, as to its cause, Who is act by His Essence. Therefore God is the cause of every action, in so far as it is an action. But sin denotes a being and an action with a defect: and this defect is from the created cause, viz. the free-will, as falling away from the order of the First Agent, viz. God. Consequently this defect is not reduced to God as its cause, but to the free-will: even as the defect of limping is reduced to a crooked leg as its cause, but not to the motive power, which nevertheless causes whatever there is of movement in the limping. Accordingly God is the cause of the act of sin: and yet He is not the cause of sin, because He does not cause the act to have a defect.
Reply to Objection: 1. In this passage Augustine calls by the name of "thing," that which is a thing simply, viz. substance; for in this sense the act of sin is not a thing.
2. Not only the act, but also the defect, is reduced to man as its cause, which defect consists in man not being subject to Whom he ought to be, although he does not intend this principally. Wherefore man is the cause of the sin: while God is the cause of the act, in such a way, that nowise is He the cause of the defect accompanying the act, so that He is not the cause of the sin.
3. As stated above (Question , Article ), acts and habits do not take their species from the privation itself, wherein consists the nature of evil, but from some object, to which that privation is united: and so this defect which consists in not being from God, belongs to the species of the act consequently, and not as a specific difference.
Objection: 1. It would seem that God is not the cause of spiritual blindness and hardness of heart. For Augustine says (Qq. lxxxiii, qu. 3) that God is not the cause of that which makes man worse. Now man is made worse by spiritual blindness and hardness of heart. Therefore God is not the cause of spiritual blindness and hardness of heart.
2. Further, Fulgentius says (De Dupl. Praedest. i, 19): "God does not punish what He causes." Now God punishes the hardened heart, according to Si 3,27: "A hard heart shall fear evil at the last." Therefore God is not the cause of hardness of heart.
3. Further, the same effect is not put down to contrary causes. But the cause of spiritual blindness is said to be the malice of man, according to Sg 2,21: "For their own malice blinded them," and again, according to 2Co 4,4: "The god of this world hath blinded the minds of unbelievers": which causes seem to be opposed to God. Therefore God is not the cause of spiritual blindness and hardness of heart.
On the contrary It is written (Is 6,10): "Blind the heart of this people, and make their ears heavy," and Rm 9,18: "He hath mercy on whom He will, and whom He will He hardeneth."
I answer that Spiritual blindness and hardness of heart imply two things. One is the movement of the human mind in cleaving to evil, and turning away from the Divine light; and as regards this, God is not the cause of spiritual blindness and hardness of heart, just as He is not the cause of sin. The other thing is the withdrawal of grace, the result of which is that the mind is not enlightened by God to see aright, and man's heart is not softened to live aright; and as regards this God is the cause of spiritual blindness and hardness of heart.Now we must consider that God is the universal cause of the enlightening of souls, according to Jn 1,9: "That was the true light which enlighteneth every man that cometh into this world," even as the sun is the universal cause of the enlightening of bodies, though not in the same way; for the sun enlightens by necessity of nature, whereas God works freely, through the order of His wisdom. Now although the sun, so far as it is concerned, enlightens all bodies, yet if it be encountered by an obstacle in a body, it leaves it in darkness, as happens to a house whose window-shutters are closed, although the sun is in no way the cause of the house being darkened, since it does not act of its own accord in failing to light up the interior of the house; and the cause of this is the person who closed the shutters. On the other hand, God, of His own accord, withholds His grace from those in whom He finds an obstacle: so that the cause of grace being withheld is not only the man who raises an obstacle to grace; but God, Who, of His own accord, withholds His grace. In this way, God is the cause of spiritual blindness, deafness of ear, and hardness of heart.These differ from one another in respect of the effects of grace, which both perfects the intellect by the gift of wisdom, and softens the affections by the fire of charity. And since two of the senses excel in rendering service to the intellect, viz. sight and hearing, of which the former assists "discovery," and the latter, "teaching," hence it is that spiritual "blindness" corresponds to sight, "heaviness of the ears" to hearing, and "hardness of heart" to the affections.
Reply to Objection: 1. Blindness and hardheartedness, as regards the withholding of grace, are punishments, and therefore, in this respect, they make man no worse. It is because he is already worsened by sin that he incurs them, even as other punishments.
2. This argument considers hardheartedness in so far as it is a sin.
3. Malice is the demeritorious cause of blindness, just as sin is the cause of punishment: and in this way too, the devil is said to blind, in so far as he induces man to sin.
Summa Th. I-II EN Qu.77 a.8