Summa Theologica, by St. Thomas Aquinas, , at sacred-texts.com
We now consider the action of the angels on man, and inquire: (1) How far they can change them by their own natural power; (2) How they are sent by God to the ministry of men; (3) How they guard and protect men.
Under the first head there are four points of inquiry:
(1) Whether an angel can enlighten the human intellect?
(2) Whether he can change man's will?
(3) Whether he can change man's imagination?
(4) Whether he can change man's senses?
Objection 1: It would seem that an angel cannot enlighten man. For man is enlightened by faith; hence Dionysius (Eccl. Hier. iii) attributes enlightenment to baptism, as "the sacrament of faith." But faith is immediately from God, according to Eph. 2:8: "By grace you are saved through faith, and that not of yourselves, for it is the gift of God." Therefore man is not enlightened by an angel; but immediately by God.
Objection 2: Further, on the words, "God hath manifested it to them" (Rom. 1:19), the gloss observes that "not only natural reason availed for the manifestation of Divine truths to men, but God also revealed them by His work," that is, by His creature. But both are immediately from God---that is, natural reason and the creature. Therefore God enlightens man immediately.
Objection 3: Further, whoever is enlightened is conscious of being enlightened. But man is not conscious of being enlightened by angels. Therefore he is not enlightened by them.
On the contrary, Dionysius says (Coel. Hier. iv) that the revelation of Divine things reaches men through the ministry of the angels. But such revelation is an enlightenment as we have stated (Q, A; Q, A). Therefore men are enlightened by the angels.
I answer that, Since the order of Divine Providence disposes that lower things be subject to the actions of higher, as explained above (Q, A); as the inferior angels are enlightened by the superior, so men, who are inferior to the angels, are enlightened by them.
The modes of each of these kinds of enlightenment are in one way alike and in another way unlike. For, as was shown above (Q, A), the enlightenment which consists in making known Divine truth has two functions; namely, according as the inferior intellect is strengthened by the action of the superior intellect, and according as the intelligible species which are in the superior intellect are proposed to the inferior so as to be grasped thereby. This takes place in the angels when the superior angel divides his universal concept of the truth according to the capacity of the inferior angel, as explained above (Q, A).
The human intellect, however, cannot grasp the universal truth itself unveiled; because its nature requires it to understand by turning to the phantasms, as above explained (Q, A). So the angels propose the intelligible truth to men under the similitudes of sensible things, according to what Dionysius says (Coel. Hier. i), that, "It is impossible for the divine ray to shine on us, otherwise than shrouded by the variety of the sacred veils." On the other hand, the human intellect as the inferior, is strengthened by the action of the angelic intellect. And in these two ways man is enlightened by an angel.
Reply to Objection 1: Two dispositions concur in the virtue of faith; first, the habit of the intellect whereby it is disposed to obey the will tending to Divine truth. For the intellect assents to the truth of faith, not as convinced by the reason, but as commanded by the will; hence Augustine says, "No one believes except willingly." In this respect faith comes from God alone. Secondly, faith requires that what is to be believed be proposed to the believer; which is accomplished by man, according to Rom. 10:17, "Faith cometh by hearing"; principally, however, by the angels, by whom Divine things are revealed to men. Hence the angels have some part in the enlightenment of faith. Moreover, men are enlightened by the angels not only concerning what is to be believed; but also as regards what is to be done.
Reply to Objection 2: Natural reason, which is immediately from God, can be strengthened by an angel, as we have said above. Again, the more the human intellect is strengthened, so much higher an intelligible truth can be elicited from the species derived from creatures. Thus man is assisted by an angel so that he may obtain from creatures a more perfect knowledge of God.
Reply to Objection 3: Intellectual operation and enlightenment can be understood in two ways. First, on the part of the object understood; thus whoever understands or is enlightened, knows that he understands or is enlightened, because he knows that the object is made known to him. Secondly, on the part of the principle; and thus it does not follow that whoever understands a truth, knows what the intellect is, which is the principle of the intellectual operation. In like manner not everyone who is enlightened by an angel, knows that he is enlightened by him.
Objection 1: It would seem that the angels can change the will of man. For, upon the text, "Who maketh His angels spirits and His ministers a flame of fire" (Heb. 1:7), the gloss notes that "they are fire, as being spiritually fervent, and as burning away our vices." This could not be, however, unless they changed the will. Therefore the angels can change the will.
Objection 2: Further, Bede says (Super Matth. xv, 11), that, "the devil does not send wicked thoughts, but kindles them." Damascene, however, says that he also sends them; for he remarks that "every malicious act and unclean passion is contrived by the demons and put into men" (De Fide Orth. ii, 4); in like manner also the good angels introduce and kindle good thoughts. But this could only be if they changed the will. Therefore the will is changed by them.
Objection 3: Further, the angel, as above explained, enlightens the human intellect by means of the phantasms. But as the imagination which serves the intellect can be changed by an angel, so can the sensitive appetite which serves the will, because it also is a faculty using a corporeal organ. Therefore as the angel enlightens the mind, so can he change the will.
On the contrary, To change the will belongs to God alone, according to Prov. 21:1: "The heart of the king is in the hand of the Lord, whithersoever He will He shall turn it."
I answer that, The will can be changed in two ways. First, from within; in which way, since the movement of the will is nothing but the inclination of the will to the thing willed, God alone can thus change the will, because He gives the power of such an inclination to the intellectual nature. For as the natural inclination is from God alone Who gives the nature, so the inclination of the will is from God alone, Who causes the will.
Secondly, the will is moved from without. As regards an angel, this can be only in one way---by the good apprehended by the intellect. Hence in as far as anyone may be the cause why anything be apprehended as an appetible good, so far does he move the will. In this way also God alone can move the will efficaciously; but an angel and man move the will by way of persuasion, as above explained (Q, A).
In addition to this mode the human will can be moved from without in another way; namely, by the passion residing in the sensitive appetite: thus by concupiscence or anger the will is inclined to will something. In this manner the angels, as being able to rouse these passions, can move the will, not however by necessity, for the will ever remains free to consent to, or to resist, the passion.
Reply to Objection 1: Those who act as God's ministers, either men or angels, are said to burn away vices, and to incite to virtue by way of persuasion.
Reply to Objection 2: The demon cannot put thoughts in our minds by causing them from within, since the act of the cogitative faculty is subject to the will; nevertheless the devil is called the kindler of thoughts, inasmuch as he incites to thought, by the desire of the things thought of, by way of persuasion, or by rousing the passions. Damascene calls this kindling "a putting in" because such a work is accomplished within. But good thoughts are attributed to a higher principle, namely, God, though they may be procured by the ministry of the angels.
Reply to Objection 3: The human intellect in its present state can understand only by turning to the phantasms; but the human will can will something following the judgment of reason rather than the passion of the sensitive appetite. Hence the comparison does not hold.
Objection 1: It would seem that an angel cannot change man's imagination. For the phantasy, as is said De Anima iii, is "a motion caused by the sense in act." But if this motion were caused by an angel, it would not be caused by the sense in act. Therefore it is contrary to the nature of the phantasy, which is the act of the imaginative faculty, to be changed by an angel.
Objection 2: Further, since the forms in the imagination are spiritual, they are nobler than the forms existing in sensible matter. But an angel cannot impress forms upon sensible matter (Q, A). Therefore he cannot impress forms on the imagination, and so he cannot change it.
Objection 3: Further, Augustine says (Gen. ad lit. xii, 12): "One spirit by intermingling with another can communicate his knowledge to the other spirit by these images, so that the latter either understands it himself, or accepts it as understood by the other." But it does not seem that an angel can be mingled with the human imagination, nor that the imagination can receive the knowledge of an angel. Therefore it seems that an angel cannot change the imagination.
Objection 4: Further, in the imaginative vision man cleaves to the similitudes of the things as to the things themselves. But in this there is deception. So as a good angel cannot be the cause of deception, it seems that he cannot cause the imaginative vision, by changing the imagination.
On the contrary, Those things which are seen in dreams are seen by imaginative vision. But the angels reveal things in dreams, as appears from Mat. 1:20;:13, in regard to the angel who appeared to Joseph in dreams. Therefore an angel can move the imagination.
I answer that, Both a good and a bad angel by their own natural power can move the human imagination. This may be explained as follows. For it was said above (Q, A), that corporeal nature obeys the angel as regards local movement, so that whatever can be caused by the local movement of bodies is subject to the natural power of the angels. Now it is manifest that imaginative apparitions are sometimes caused in us by the local movement of animal spirits and humors. Hence Aristotle says (De Somn. et Vigil.) [*De Insomniis iii.], when assigning the cause of visions in dreams, that "when an animal sleeps, the blood descends in abundance to the sensitive principle, and movements descend with it," that is, the impressions left from the movements are preserved in the animal spirits, "and move the sensitive principle"; so that a certain appearance ensues, as if the sensitive principle were being then changed by the external objects themselves. Indeed, the commotion of the spirits and humors may be so great that such appearances may even occur to those who are awake, as is seen in mad people, and the like. So, as this happens by a natural disturbance of the humors, and sometimes also by the will of man who voluntarily imagines what he previously experienced, so also the same may be done by the power of a good or a bad angel, sometimes with alienation from the bodily senses, sometimes without such alienation.
Reply to Objection 1: The first principle of the imagination is from the sense in act. For we cannot imagine what we have never perceived by the senses, either wholly or partly; as a man born blind cannot imagine color. Sometimes, however, the imagination is informed in such a way that the act of the imaginative movement arises from the impressions preserved within.
Reply to Objection 2: An angel changes the imagination, not indeed by the impression of an imaginative form in no way previously received from the senses (for he cannot make a man born blind imagine color), but by local movement of the spirits and humors, as above explained.
Reply to Objection 3: The commingling of the angelic spirit with the human imagination is not a mingling of essences, but by reason of an effect which he produces in the imagination in the way above stated; so that he shows man what he [the angel] knows, but not in the way he knows.
Reply to Objection 4: An angel causing an imaginative vision, sometimes enlightens the intellect at the same time, so that it knows what these images signify; and then there is not deception. But sometimes by the angelic operation the similitudes of things only appear in the imagination; but neither then is deception caused by the angel, but by the defect in the intellect to whom such things appear. Thus neither was Christ a cause of deception when He spoke many things to the people in parables, which He did not explain to them.
Objection 1: It seems that an angel cannot change the human senses. For the sensitive operation is a vital operation. But such an operation does not come from an extrinsic principle. Therefore the sensitive operation cannot be caused by an angel.
Objection 2: Further, the sensitive operation is nobler than the nutritive. But the angel cannot change the nutritive power, nor other natural forms. Therefore neither can he change the sensitive power.
Objection 3: Further, the senses are naturally moved by the sensible objects. But an angel cannot change the order of nature (Q, A). Therefore an angel cannot change the senses; but these are changed always by the sensible object.
On the contrary, The angels who overturned Sodom, "struck the people of Sodom with blindness or , so that they could not find the door" (Gn. 19:11). [*It is worth noting that these are the only two passages in the Greek version where the word appears. It expresses, in fact, the effect produced on the people of Sodom---namely, dazzling (French version, "eblouissement"), which the Latin "caecitas" (blindness) does not necessarily imply.] The same is recorded of the Syrians whom Eliseus led into Samaria (4 Kings 6:18).
I answer that, The senses may be changed in a twofold manner; from without, as when affected by the sensible object: and from within, for we see that the senses are changed when the spirits and humors are disturbed; as for example, a sick man's tongue, charged with choleric humor, tastes everything as bitter, and the like with the other senses. Now an angel, by his natural power, can work a change in the senses both ways. For an angel can offer the senses a sensible object from without, formed by nature or by the angel himself, as when he assumes a body, as we have said above (Q, A). Likewise he can move the spirits and humors from within, as above remarked, whereby the senses are changed in various ways.
Reply to Objection 1: The principle of the sensitive operation cannot be without the interior principle which is the sensitive power; but this interior principle can be moved in many ways by the exterior principle, as above explained.
Reply to Objection 2: By the interior movement of the spirits and humors an angel can do something towards changing the act of the nutritive power, and also of the appetitive and sensitive power, and of any other power using a corporeal organ.
Reply to Objection 3: An angel can do nothing outside the entire order of creatures; but he can outside some particular order of nature, since he is not subject to that order; thus in some special way an angel can work a change in the senses outside the common mode of nature.