Summa Th. I-II EN Qu.109 a.9

Whether one who has already obtained grace, can, of himself and without further help of grace, do good and avoid sin?


Objection: 1. It would seem that whoever has already obtained grace, can by himself and without further help of grace, do good and avoid sin. For a thing is useless or imperfect, if it does not fulfil what it was given for. Now grace is given to us that we may do good and keep from sin. Hence if with grace man cannot do this, it seems that grace is either useless or imperfect.
Further, by grace the Holy Spirit dwells in us, according to 1Co 3,16: "Know you not that you are the temple of God, and that the Spirit of God dwelleth in you?" Now since the Spirit of God is omnipotent, He is sufficient to ensure our doing good and to keep us from sin. Hence a man who has obtained grace can do the above two things without any further assistance of grace.
3. Further, if a man who has obtained grace needs further aid of grace in order to live righteously and to keep free from sin, with equal reason, will he need yet another grace, even though he has obtained this first help of grace. Therefore we must go on to infinity; which is impossible. Hence whoever is in grace needs no further help of grace in order to do righteously and to keep free from sin.

On the contrary
Augustine says (De Natura et Gratia xxvi) that "as the eye of the body though most healthy cannot see unless it is helped by the brightness of light, so, neither can a man, even if he is most righteous, live righteously unless he be helped by the eternal light of justice." But justification is by grace, according to Rm 3,24: "Being justified freely by His grace." Hence even a man who already possesses grace needs a further assistance of grace in order to live righteously.
I answer that As stated above (Article [5]), in order to live righteously a man needs a twofold help of God---first, a habitual gift whereby corrupted human nature is healed, and after being healed is lifted up so as to work deeds meritoriously of everlasting life, which exceed the capability of nature. Secondly, man needs the help of grace in order to be moved by God to act.
Now with regard to the first kind of help, man does not need a further help of grace, e.g. a further infused habit. Yet he needs the help of grace in another way, i.e. in order to be moved by God to act righteously, and this for two reasons: first, for the general reason that no created thing can put forth any act, unless by virtue of the Divine motion. Secondly, for this special reason---the condition of the state of human nature. For although healed by grace as to the mind, yet it remains corrupted and poisoned in the flesh, whereby it serves "the law of sin,"
Rm 7,25. In the intellect, too, there seems the darkness of ignorance, whereby, as is written (Rm 8,26): "We know not what we should pray for as we ought"; since on account of the various turns of circumstances, and because we do not know ourselves perfectly, we cannot fully know what is for our good, according to Sg 9,14: "For the thoughts of mortal men are fearful and our counsels uncertain." Hence we must be guided and guarded by God, Who knows and can do all things. For which reason also it is becoming in those who have been born again as sons of God, to say: "Lead us not into temptation," and "Thy Will be done on earth as it is in heaven," and whatever else is contained in the Lord's Prayer pertaining to this.

Reply to Objection: 1. The gift of habitual grace is not therefore given to us that we may no longer need the Divine help; for every creature needs to be preserved in the good received from Him. Hence if after having received grace man still needs the Divine help, it cannot be concluded that grace is given to no purpose, or that it is imperfect, since man will need the Divine help even in the state of glory, when grace shall be fully perfected. But here grace is to some extent imperfect, inasmuch as it does not completely heal man, as stated above.
The operation of the Holy Ghost, which moves and protects, is not circumscribed by the effect of habitual grace which it causes in us; but beyond this effect He, together with the Father and the Son, moves and protects us.
This argument merely proves that man needs no further habitual grace.

Whether man possessed of grace needs the help of grace in order to persevere?


Objection: 1. It would seem that man possessed of grace needs no help to persevere. For perseverance is something less than virtue, even as continence is, as is clear from the Philosopher (Ethic. vii, 7,9). Now since man is justified by grace, he needs no further help of grace in order to have the virtues. Much less, therefore, does he need the help of grace to have perseverance.
Further, all the virtues are infused at once. But perseverance is put down as a virtue. Hence it seems that, together with grace, perseverance is given to the other infused virtues.
Further, as the Apostle says (Rm 5,20) more was restored to man by Christ's gift, than he had lost by Adam's sin. But Adam received what enabled him to persevere; and thus man does not need grace in order to persevere.

On the contrary Augustine says (De Persev. ii): "Why is perseverance besought of God, if it is not bestowed by God? For is it not a mocking request to seek what we know He does not give, and what is in our power without His giving it?" Now perseverance is besought by even those who are hallowed by grace; and this is seen, when we say "Hallowed be Thy name," which Augustine confirms by the words of Cyprian (De Correp. et Grat. xii). Hence man, even when possessed of grace, needs perseverance to be given to him by God.
I answer that
Perseverance is taken in three ways. First, to signify a habit of the mind whereby a man stands steadfastly, lest he be moved by the assault of sadness from what is virtuous. And thus perseverance is to sadness as continence is to concupiscence and pleasure, as the Philosopher says (Ethic. vii, 7). Secondly, perseverance may be called a habit, whereby a man has the purpose of persevering in good unto the end. And in both these ways perseverance is infused together with grace, even as continence and the other virtues are. Thirdly, perseverance is called the abiding in good to the end of life. And in order to have this perseverance man does not, indeed, need another habitual grace, but he needs the Divine assistance guiding and guarding him against the attacks of the passions, as appears from the preceding article. And hence after anyone has been justified by grace, he still needs to beseech God for the aforesaid gift of perseverance, that he may be kept from evil till the end of his life. For to many grace is given to whom perseverance in grace is not given.

Reply to Objection: 1.
This objection regards the first mode of perseverance, as the second objection regards the second.
Hence the solution of the second objection is clear.
As Augustine says (De Natura et Gratia xliii) [*Cf. De Correp. et Grat. xii]: "in the original state man received a gift whereby he could persevere, but to persevere was not given him. But now, by the grace of Christ, many receive both the gift of grace whereby they may persevere, and the further gift of persevering," and thus Christ's gift is greater than Adam's fault. Nevertheless it was easier for man to persevere, with the gift of grace in the state of innocence in which the flesh was not rebellious against the spirit, than it is now. For the restoration by Christ's grace, although it is already begun in the mind, is not yet completed in the flesh, as it will be in heaven, where man will not merely be able to persevere but will be unable to sin.



We must now consider the grace of God as regards its essence; and under this head there are four points of inquiry:

(1) Whether grace implies something in the soul?

(2) Whether grace is a quality?

(3) Whether grace differs from infused virtue?

(4) Of the subject of grace.

Whether grace implies anything in the soul?


Objection: 1. It would seem that grace does not imply anything in the soul. For man is said to have the grace of God even as the grace of man. Hence it is written (
Gn 39,21) that the Lord gave to Joseph "grace [Douay: 'favor'] in the sight of the chief keeper of the prison." Now when we say that a man has the favor of another, nothing is implied in him who has the favor of the other, but an acceptance is implied in him whose favor he has. Hence when we say that a man has the grace of God, nothing is implied in his soul; but we merely signify the Divine acceptance.
2. Further, as the soul quickens the body so does God quicken the soul; hence it is written (Dt 30,20): "He is thy life." Now the soul quickens the body immediately. Therefore nothing can come as a medium between God and the soul. Hence grace implies nothing created in the soul.
3. Further, on Rm 1,7, "Grace to you and peace," the gloss says: "Grace, i.e. the remission of sins." Now the remission of sin implies nothing in the soul, but only in God, Who does not impute the sin, according to Ps 31,2: "Blessed is the man to whom the Lord hath not imputed sin." Hence neither does grace imply anything in the soul.

On the contrary Light implies something in what is enlightened. But grace is a light of the soul; hence Augustine says (De Natura et Gratia xxii): "The light of truth rightly deserts the prevaricator of the law, and those who have been thus deserted become blind." Therefore grace implies something in the soul.
I answer that
According to the common manner of speech, grace is usually taken in three ways. First, for anyone's love, as we are accustomed to say that the soldier is in the good graces of the king, i.e. the king looks on him with favor. Secondly, it is taken for any gift freely bestowed, as we are accustomed to say: I do you this act of grace. Thirdly, it is taken for the recompense of a gift given "gratis," inasmuch as we are said to be "grateful" for benefits. Of these three the second depends on the first, since one bestows something on another "gratis" from the love wherewith he receives him into his good "graces." And from the second proceeds the third, since from benefits bestowed "gratis" arises "gratitude."Now as regards the last two, it is clear that grace implies something in him who receives grace: first, the gift given gratis; secondly, the acknowledgment of the gift. But as regards the first, a difference must be noted between the grace of God and the grace of man; for since the creature's good springs from the Divine will, some good in the creature flows from God's love, whereby He wishes the good of the creature. On the other hand, the will of man is moved by the good pre-existing in things; and hence man's love does not wholly cause the good of the thing, but pre-supposes it either in part or wholly. Therefore it is clear that every love of God is followed at some time by a good caused in the creature, but not co-eternal with the eternal love. And according to this difference of good the love of God to the creature is looked at differently. For one is common, whereby He loves "all things that are" (Sg 11,25), and thereby gives things their natural being. But the second is a special love, whereby He draws the rational creature above the condition of its nature to a participation of the Divine good; and according to this love He is said to love anyone simply, since it is by this love that God simply wishes the eternal good, which is Himself, for the creature.Accordingly when a man is said to have the grace of God, there is signified something bestowed on man by God. Nevertheless the grace of God sometimes signifies God's eternal love, as we say the grace of predestination, inasmuch as God gratuitously and not from merits predestines or elects some; for it is written (Ep 1,5): "He hath predestinated us into the adoption of children . . . unto the praise of the glory of His grace."

Reply to Objection: 1. Even when a man is said to be in another's good graces, it is understood that there is something in him pleasing to the other; even as anyone is said to have God's grace---with this difference, that what is pleasing to a man in another is presupposed to his love, but whatever is pleasing to God in a man is caused by the Divine love, as was said above.
God is the life of the soul after the manner of an efficient cause; but the soul is the life of the body after the manner of a formal cause. Now there is no medium between form and matter, since the form, of itself, "informs" the matter or subject; whereas the agent "informs" the subject, not by its substance, but by the form, which it causes in the matter.
Augustine says (Retract. i, 25): "When I said that grace was for the remission of sins, and peace for our reconciliation with God, you must not take it to mean that peace and reconciliation do not pertain to general peace, but that the special name of grace signifies the remission of sins." Not only grace, therefore, but many other of God's gifts pertain to grace. And hence the remission of sins does not take place without some effect divinely caused in us, as will appear later (Question [113], Article [2]).

Whether grace is a quality of the soul?


Objection: 1. It would seem that grace is not a quality of the soul. For no quality acts on its subject, since the action of a quality is not without the action of its subject, and thus the subject would necessarily act upon itself. But grace acts upon the soul, by justifying it. Therefore grace is not a quality.
Furthermore, substance is nobler than quality. But grace is nobler than the nature of the soul, since we can do many things by grace, to which nature is not equal, as stated above (Question [109], Articles [1],2,3). Therefore grace is not a quality.
Furthermore, no quality remains after it has ceased to be in its subject. But grace remains; since it is not corrupted, for thus it would be reduced to nothing, since it was created from nothing; hence it is called a "new creature"(Ga 6,15).

On the contrary on Ps 103,15: "That he may make the face cheerful with oil"; the gloss says: "Grace is a certain beauty of soul, which wins the Divine love." But beauty of soul is a quality, even as beauty of body. Therefore grace is a quality.
I answer that As stated above (Article [1]), there is understood to be an effect of God's gratuitous will in whoever is said to have God's grace. Now it was stated (Question [109], Article [1]) that man is aided by God's gratuitous will in two ways: first, inasmuch as man's soul is moved by God to know or will or do something, and in this way the gratuitous effect in man is not a quality, but a movement of the soul; for "motion is the act of the mover in the moved." Secondly, man is helped by God's gratuitous will, inasmuch as a habitual gift is infused by God into the soul; and for this reason, that it is not fitting that God should provide less for those He loves, that they may acquire supernatural good, than for creatures, whom He loves that they may acquire natural good. Now He so provides for natural creatures, that not merely does He move them to their natural acts, but He bestows upon them certain forms and powers, which are the principles of acts, in order that they may of themselves be inclined to these movements, and thus the movements whereby they are moved by God become natural and easy to creatures, according to Sg 8,1: "she . . . ordereth all things sweetly." Much more therefore does He infuse into such as He moves towards the acquisition of supernatural good, certain forms or supernatural qualities, whereby they may be moved by Him sweetly and promptly to acquire eternal good; and thus the gift of grace is a quality.

Reply to Objection: 1. Grace, as a quality, is said to act upon the soul, not after the manner of an efficient cause, but after the manner of a formal cause, as whiteness makes a thing white, and justice, just.
Every substance is either the nature of the thing whereof it is the substance or is a part of the nature, even as matter and form are called substance. And because grace is above human nature, it cannot be a substance or a substantial form, but is an accidental form of the soul. Now what is substantially in God, becomes accidental in the soul participating the Divine goodness, as is clear in the case of knowledge. And thus because the soul participates in the Divine goodness imperfectly, the participation of the Divine goodness, which is grace, has its being in the soul in a less perfect way than the soul subsists in itself. Nevertheless, inasmuch as it is the expression or participation of the Divine goodness, it is nobler than the nature of the soul, though not in its mode of being.
As Boethius [*Pseudo-Bede, Sent. Phil. ex Artist] says, the "being of an accident is to inhere." Hence no accident is called being as if it had being, but because by it something is; hence it is said to belong to a being rather to be a being (Metaph. vii, text. 2). And because to become and to be corrupted belong to what is, properly speaking, no accident comes into being or is corrupted, but is said to come into being and to be corrupted inasmuch as its subject begins or ceases to be in act with this accident. And thus grace is said to be created inasmuch as men are created with reference to it, i.e. are given a new being out of nothing, i.e. not from merits, according to Ep 2,10, "created in Jesus Christ in good works."

Whether grace is the same as virtue?


Objection: 1. It would seem that grace is the same as virtue. For Augustine says (De Spir. et Lit. xiv) that "operating grace is faith that worketh by charity." But faith that worketh by charity is a virtue. Therefore grace is a virtue.
Further, what fits the definition, fits the defined. But the definitions of virtue given by saints and philosophers fit grace, since "it makes its subject good, and his work good," and "it is a good quality of the mind, whereby we live righteously," etc. Therefore grace is virtue.
Further, grace is a quality. Now it is clearly not in the "fourth" species of quality; viz. "form" which is the "abiding figure of things," since it does not belong to bodies. Nor is it in the "third," since it is not a "passion nor a passion-like quality," which is in the sensitive part of the soul, as is proved in Physic. viii; and grace is principally in the mind. Nor is it in the "second" species, which is "natural power" or "impotence"; since grace is above nature and does not regard good and evil, as does natural power. Therefore it must be in the "first" species which is "habit" or "disposition." Now habits of the mind are virtues; since even knowledge itself is a virtue after a manner, as stated above (Question [57], Articles [1],2). Therefore grace is the same as virtue.

On the contrary
If grace is a virtue, it would seem before all to be one of the three theological virtues. But grace is neither faith nor hope, for these can be without sanctifying grace. Nor is it charity, since "grace foreruns charity," as Augustine says in his book on the Predestination of the Saints (De Dono Persev. xvi). Therefore grace is not virtue.
I answer that
Some held that grace and virtue were identical in essence, and differed only logically---in the sense that we speak of grace inasmuch as it makes man pleasing to God, or is given gratuitously---and of virtue inasmuch as it empowers us to act rightly. And the Master seems to have thought this (Sent. ii, D 27).But if anyone rightly considers the nature of virtue, this cannot hold, since, as the Philosopher says (Physic. vii, text. 17), "virtue is disposition of what is perfect---and I call perfect what is disposed according to its nature." Now from this it is clear that the virtue of a thing has reference to some pre-existing nature, from the fact that everything is disposed with reference to what befits its nature. But it is manifest that the virtues acquired by human acts of which we spoke above (Question [55], seqq.) are dispositions, whereby a man is fittingly disposed with reference to the nature whereby he is a man; whereas infused virtues dispose man in a higher manner and towards a higher end, and consequently in relation to some higher nature, i.e. in relation to a participation of the Divine Nature, according to 2P 1,4: "He hath given us most great and most precious promises; that by these you may be made partakers of the Divine Nature." And it is in respect of receiving this nature that we are said to be born again sons of God.And thus, even as the natural light of reason is something besides the acquired virtues, which are ordained to this natural light, so also the light of grace which is a participation of the Divine Nature is something besides the infused virtues which are derived from and are ordained to this light, hence the Apostle says (Ep 5,8): "For you were heretofore darkness, but now light in the Lord. Walk then as children of the light." For as the acquired virtues enable a man to walk, in accordance with the natural light of reason, so do the infused virtues enable a man to walk as befits the light of grace.

Reply to Objection: 1. Augustine calls "faith that worketh by charity" grace, since the act of faith of him that worketh by charity is the first act by which sanctifying grace is manifested.
Good is placed in the definition of virtue with reference to its fitness with some pre-existing nature essential or participated. Now good is not attributed to grace in this manner, but as to the root of goodness in man, as stated above.
Grace is reduced to the first species of quality; and yet it is not the same as virtue, but is a certain disposition which is presupposed to the infused virtues, as their principle and root.

Whether grace is in the essence of the soul as in a subject, or in one of the powers?


Objection: 1. It would seem that grace is not in the essence of the soul, as in a subject, but in one of the powers. For Augustine says (Hypognosticon iii [*Among the spurious works of St. Augustine]) that grace is related to the will or to the free will "as a rider to his horse." Now the will or the free will is a power, as stated above (
I 83,2). Hence grace is in a power of the soul, as in a subject.
2. Further, "Man's merit springs from grace" as Augustine says (De Gratia et Lib. Arbit. vi). Now merit consists in acts, which proceed from a power. Hence it seems that grace is a perfection of a power of the soul.
Further, if the essence of the soul is the proper subject of grace, the soul, inasmuch as it has an essence, must be capable of grace. But this is false; since it would follow that every soul would be capable of grace. Therefore the essence of the soul is not the proper subject of grace.
Further, the essence of the soul is prior to its powers. Now what is prior may be understood without what is posterior. Hence it follows that grace may be taken to be in the soul, although we suppose no part or power of the soul---viz. neither the will, nor the intellect, nor anything else; which is impossible.

On the contrary
By grace we are born again sons of God. But generation terminates at the essence prior to the powers. Therefore grace is in the soul's essence prior to being in the powers.
I answer that
This question depends on the preceding. For if grace is the same as virtue, it must necessarily be in the powers of the soul as in a subject; since the soul's powers are the proper subject of virtue, as stated above (Question [56], Article [1]). But if grace differs from virtue, it cannot be said that a power of the soul is the subject of grace, since every perfection of the soul's powers has the nature of virtue, as stated above (Question [55], Article [1]; Question [56], Article [1]). Hence it remains that grace, as it is prior to virtue, has a subject prior to the powers of the soul, so that it is in the essence of the soul. For as man in his intellective powers participates in the Divine knowledge through the virtue of faith, and in his power of will participates in the Divine love through the virtue of charity, so also in the nature of the soul does he participate in the Divine Nature, after the manner of a likeness, through a certain regeneration or re-creation.

Reply to Objection: 1.
As from the essence of the soul flows its powers, which are the principles of deeds, so likewise the virtues, whereby the powers are moved to act, flow into the powers of the soul from grace. And thus grace is compared to the will as the mover to the moved, which is the same comparison as that of a horseman to the horse---but not as an accident to a subject.
And thereby is made clear the Reply to the Second Objection. For grace is the principle of meritorious works through the medium of virtues, as the essence of the soul is the principal of vital deeds through the medium of the powers.
The soul is the subject of grace, as being in the species of intellectual or rational nature. But the soul is not classed in a species by any of its powers, since the powers are natural properties of the soul following upon the species. Hence the soul differs specifically in its essence from other souls, viz. of dumb animals, and of plants. Consequently it does not follow that, if the essence of the human soul is the subject of grace, every soul may be the subject of grace; since it belongs to the essence of the soul, inasmuch as it is of such a species.
Since the powers of the soul are natural properties following upon the species, the soul cannot be without them. Yet, granted that it was without them, the soul would still be called intellectual or rational in its species, not that it would actually have these powers, but on account of the essence of such a species, from which these powers naturally flow.



We must now consider the division of grace; under which head there are five points of inquiry:

(1) Whether grace is fittingly divided into gratuitous grace and sanctifying grace?

(2) Of the division into operating and cooperating grace;

(3) Of the division of it into prevenient and subsequent grace;

(4) Of the division of gratuitous grace;

(5) Of the comparison between sanctifying and gratuitous grace.

Whether grace is fittingly divided into sanctifying grace and gratuitous grace?


Objection: 1. It would seem that grace is not fittingly divided into sanctifying grace and gratuitous grace. For grace is a gift of God, as is clear from what has been already stated (Question [110], Article [1]). But man is not therefore pleasing to God because something is given him by God, but rather on the contrary; since something is freely given by God, because man is pleasing to Him. Hence there is no sanctifying grace.
Further, whatever is not given on account of preceding merits is given gratis. Now even natural good is given to man without preceding merit, since nature is presupposed to merit. Therefore nature itself is given gratuitously by God. But nature is condivided with grace. Therefore to be gratuitously given is not fittingly set down as a difference of grace, since it is found outside the genus of grace.
Further, members of a division are mutually opposed. But even sanctifying grace, whereby we are justified, is given to us gratuitously, according to Rm 3,24: "Being justified freely [gratis] by His grace." Hence sanctifying grace ought not to be divided against gratuitous grace.

On the contrary The Apostle attributes both to grace, viz. to sanctify and to be gratuitously given. For with regard to the first he says (Ep 1,6): "He hath graced us in His beloved son." And with regard to the second (Rm 2,6): "And if by grace, it is not now by works, otherwise grace is no more grace." Therefore grace can be distinguished by its having one only or both.
I answer that As the Apostle says (Rm 13,1), "those things that are of God are well ordered [Vulg.: 'those that are, are ordained by God]." Now the order of things consists in this, that things are led to God by other things, as Dionysius says (Coel. Hier. iv). And hence since grace is ordained to lead men to God, this takes place in a certain order, so that some are led to God by others.And thus there is a twofold grace: one whereby man himself is united to God, and this is called "sanctifying grace"; the other is that whereby one man cooperates with another in leading him to God, and this gift is called "gratuitous grace," since it is bestowed on a man beyond the capability of nature, and beyond the merit of the person. But whereas it is bestowed on a man, not to justify him, but rather that he may cooperate in the justification of another, it is not called sanctifying grace. And it is of this that the Apostle says (1Co 12,7): "And the manifestation of the Spirit is given to every man unto utility," i.e. of others.

Reply to Objection: 1. Grace is said to make pleasing, not efficiently but formally, i.e. because thereby a man is justified, and is made worthy to be called pleasing to God, according to Col 1,21: "He hath made us worthy to be made partakers of the lot of the saints in light."
2. Grace, inasmuch as it is gratuitously given, excludes the notion of debt. Now debt may be taken in two ways: first, as arising from merit; and this regards the person whose it is to do meritorious works, according to Rm 4,4: "Now to him that worketh, the reward is not reckoned according to grace, but according to debt." The second debt regards the condition of nature. Thus we say it is due to a man to have reason, and whatever else belongs to human nature. Yet in neither way is debt taken to mean that God is under an obligation to His creature, but rather that the creature ought to be subject to God, that the Divine ordination may be fulfilled in it, which is that a certain nature should have certain conditions or properties, and that by doing certain works it should attain to something further. And hence natural endowments are not a debt in the first sense but in the second. Hence they especially merit the name of grace.
3. Sanctifying grace adds to the notion of gratuitous grace something pertaining to the nature of grace, since it makes man pleasing to God. And hence gratuitous grace which does not do this keeps the common name, as happens in many other cases; and thus the two parts of the division are opposed as sanctifying and non-sanctifying grace.

Whether grace is fittingly divided into operating and cooperating grace?


Objection: 1. It would seem that grace is not fittingly divided into operating and cooperating grace. For grace is an accident, as stated above (Question [110], Article [2]). Now no accident can act upon its subject. Therefore no grace can be called operating.
Further, if grace operates anything in us it assuredly brings about justification. But not only grace works this. For Augustine says, on Jn 14,12, "the works that I do he also shall do," says (Serm. clxix): "He Who created thee without thyself, will not justify thee without thyself." Therefore no grace ought to be called simply operating.
3. Further, to cooperate seems to pertain to the inferior agent, and not to the principal agent. But grace works in us more than free-will, according to Rm 9,16: "It is not of him that willeth, nor of him that runneth, but of God that sheweth mercy." Therefore no grace ought to be called cooperating.
4. Further, division ought to rest on opposition. But to operate and to cooperate are not opposed; for one and the same thing can both operate and cooperate. Therefore grace is not fittingly divided into operating and cooperating.

On the contrary
Augustine says (De Gratia et Lib. Arbit. xvii): "God by cooperating with us, perfects what He began by operating in us, since He who perfects by cooperation with such as are willing, beings by operating that they may will." But the operations of God whereby He moves us to good pertain to grace. Therefore grace is fittingly divided into operating and cooperating.
I answer that
As stated above (Question [110], Article [2]) grace may be taken in two ways; first, as a Divine help, whereby God moves us to will and to act; secondly, as a habitual gift divinely bestowed on us.Now in both these ways grace is fittingly divided into operating and cooperating. For the operation of an effect is not attributed to the thing moved but to the mover. Hence in that effect in which our mind is moved and does not move, but in which God is the sole mover, the operation is attributed to God, and it is with reference to this that we speak of "operating grace." But in that effect in which our mind both moves and is moved, the operation is not only attributed to God, but also to the soul; and it is with reference to this that we speak of "cooperating grace." Now there is a double act in us. First, there is the interior act of the will, and with regard to this act the will is a thing moved, and God is the mover; and especially when the will, which hitherto willed evil, begins to will good. And hence, inasmuch as God moves the human mind to this act, we speak of operating grace. But there is another, exterior act; and since it is commanded by the will, as was shown above (Question [17], Article [9]) the operation of this act is attributed to the will. And because God assists us in this act, both by strengthening our will interiorly so as to attain to the act, and by granting outwardly the capability of operating, it is with respect to this that we speak of cooperating grace. Hence after the aforesaid words Augustine subjoins: "He operates that we may will; and when we will, He cooperates that we may perfect." And thus if grace is taken for God's gratuitous motion whereby He moves us to meritorious good, it is fittingly divided into operating and cooperating grace.But if grace is taken for the habitual gift, then again there is a double effect of grace, even as of every other form; the first of which is "being," and the second, "operation"; thus the work of heat is to make its subject hot, and to give heat outwardly. And thus habitual grace, inasmuch as it heals and justifies the soul, or makes it pleasing to God, is called operating grace; but inasmuch as it is the principle of meritorious works, which spring from the free-will, it is called cooperating grace.

Reply to Objection: 1.
Inasmuch as grace is a certain accidental quality, it does not act upon the soul efficiently, but formally, as whiteness makes a surface white.
God does not justify us without ourselves, because whilst we are being justified we consent to God's justification [justitiae] by a movement of our free-will. Nevertheless this movement is not the cause of grace, but the effect; hence the whole operation pertains to grace.
One thing is said to cooperate with another not merely when it is a secondary agent under a principal agent, but when it helps to the end intended. Now man is helped by God to will the good, through the means of operating grace. And hence, the end being already intended, grace cooperates with us.
Operating and cooperating grace are the same grace; but are distinguished by their different effects, as is plain from what has been said.

Summa Th. I-II EN Qu.109 a.9