Objection 1. It would seem that no gratuitous grace is directed to the working of miracles. For every grace puts something in the one to whom it is given (Cf. I-II, 90, 1). Now the working of miracles puts nothing in the soul of the man who receives it since miracles are wrought at the touch even of a dead body. Thus we read (2 Kings 13:21) that "some... cast the body into the sepulchre of Eliseus. And when it had touched the bones of Eliseus, the man came to life, and stood upon his feet." Therefore the working of miracles does not belong to a gratuitous grace.
Objection 2. Further, the gratuitous graces are from the Holy Ghost, according to 1 Corinthians 12:4, "There are diversities of graces, but the same Spirit." Now the working of miracles is effected even by the unclean spirit, according to Matthew 24:24, "There shall arise false Christs and false prophets, and shall show great signs and wonders." Therefore it would seem that the working of miracles does not belong to a gratuitous grace.
Objection 3. Further, miracles are divided into "signs," "wonders" or "portents," and "virtues." [Cf. 2 Thessalonians 2:9, where the Douay version renders 'virtus' by 'power.' The use of the word 'virtue' in the sense of a miracle is now obsolete, and the generic term 'miracle' is elsewhere used in its stead: Cf. 1 Corinthians 12:10-28; Hebrews 2:4; Acts 2:22. Therefore it is unreasonable to reckon the "working of miracles" a gratuitous grace, any more than the "working of signs" and "wonders."
Objection 4. Further, the miraculous restoring to health is done by the power of God. Therefore the grace of healing should not be distinguished from the working of miracles.
Objection 5. Further, the working of miracles results from faith--either of the worker, according to 1 Corinthians 13:2, "If I should have all faith, so that I could remove mountains," or of other persons for whose sake miracles are wrought, according to Matthew 13:58, "And He wrought not many miracles there, because of their unbelief." Therefore, if faith be reckoned a gratuitous grace, it is superfluous to reckon in addition the working of signs as another gratuitous grace.
On the contrary, The Apostle (1 Corinthians 12:9-10) says that among other gratuitous graces, "to another" is given "the grace of healing... to another, the working of miracles."
I answer that, As stated above (Question 177, Article 1), the Holy Ghost provides sufficiently for the Church in matters profitable unto salvation, to which purpose the gratuitous graces are directed. Now just as the knowledge which a man receives from God needs to be brought to the knowledge of others through the gift of tongues and the grace of the word, so too the word uttered needs to be confirmed in order that it be rendered credible. This is done by the working of miracles, according to Mark 16:20, "And confirming the word with signs that followed": and reasonably so. For it is natural to man to arrive at the intelligible truth through its sensible effects. Wherefore just as man led by his natural reason is able to arrive at some knowledge of God through His natural effects, so is he brought to a certain degree of supernatural knowledge of the objects of faith by certain supernatural effects which are called miracles. Therefore the working of miracles belongs to a gratuitous grace.
Reply to Objection 1. Just as prophecy extends to whatever can be known supernaturally, so the working of miracles extends to all things that can be done supernaturally; the cause whereof is the divine omnipotence which cannot be communicated to any creature. Hence it is impossible for the principle of working miracles to be a quality abiding as a habit in the soul. On the other hand, just as the prophet's mind is moved by divine inspiration to know something supernaturally, so too is it possible for the mind of the miracle worker to be moved to do something resulting in the miraculous effect which God causes by His power. Sometimes this takes place after prayer, as when Peter raised to life the dead Tabitha (Acts 9:40): sometimes without any previous prayer being expressed, as when Peter by upbraiding the lying Ananias and Saphira delivered them to death (Acts 5:4-9). Hence Gregory says (Dial. ii, 30) that "the saints work miracles, sometimes by authority, sometimes by prayer." On either case, however, God is the principal worker, for He uses instrumentally either man's inward movement, or his speech, or some outward action, or again the bodily contact of even a dead body. Thus when Josue had said as though authoritatively (Joshua 10:12): "Move not, O sun, toward Gabaon," it is said afterwards (Joshua 10:14): "There was not before or after so long a day, the Lord obeying the voice of a man."
Reply to Objection 2. Our Lord is speaking there of the miracles to be wrought at the time of Antichrist, of which the Apostle says (2 Thessalonians 2:9) that the coming of Antichrist will be "according to the working of Satan, in all power, and signs, and lying wonders." To quote the words of Augustine (De Civ. Dei xx, 19), "it is a matter of debate whether they are called signs and lying wonders, because he will deceive the senses of mortals by imaginary visions, in that he will seem to do what he does not, or because, though they be real wonders, they will seduce into falsehood them that believe." They are said to be real, because the things themselves will be real, just as Pharaoh's magicians made real frogs and real serpents; but they will not be real miracles, because they will be done by the power of natural causes, as stated in I, 114, 4; whereas the working of miracles which is ascribed to a gratuitous grace, is done by God's power for man's profit.
Reply to Objection 3. Two things may be considered in miracles. One is that which is done: this is something surpassing the faculty of nature, and in this respect miracles are called "virtues." The other thing is the purpose for which miracles are wrought, namely the manifestation of something supernatural, and in this respect they are commonly called "signs": but on account of some excellence they receive the name of "wonder" or "prodigy," as showing something from afar [procul].
Reply to Objection 4. The "grace of healing" is mentioned separately, because by its means a benefit, namely bodily health, is conferred on man in addition to the common benefit bestowed in all miracles, namely the bringing of men to the knowledge of God.
Reply to Objection 5. The working of miracles is ascribed to faith for two reasons. First, because it is directed to the confirmation of faith, secondly, because it proceeds from God's omnipotence on which faith relies. Nevertheless, just as besides the grace of faith, the grace of the word is necessary that people may be instructed in the faith, so too is the grace of miracles necessary that people may be confirmed in their faith.
Source: Summa Theologica (New Advent)