Objection 1. It would seem that gratuitous grace is not rightly divided by the Apostle. For every gift vouchsafed to us by God, may be called a gratuitous grace. Now there are an infinite number of gifts freely bestowed on us by God as regards both the good of the soul and the good of the body--and yet they do not make us pleasing to God. Hence gratuitous graces cannot be contained under any certain division.
Objection 2. Further, gratuitous grace is distinguished from sanctifying grace. But faith pertains to sanctifying grace, since we are justified by it, according to Romans 5:1: "Being justified therefore by faith." Hence it is not right to place faith amongst the gratuitous graces, especially since the other virtues are not so placed, as hope and charity.
Objection 3. Further, the operation of healing, and speaking divers tongues are miracles. Again, the interpretation of speeches pertains either to wisdom or to knowledge, according to Daniel 1:17: "And to these children God gave knowledge and understanding in every book and wisdom." Hence it is not correct to divide the grace of healing and kinds of tongues against the working of miracles; and the interpretation of speeches against the word of wisdom and knowledge.
Objection 4. Further, as wisdom and knowledge are gifts of the Holy Ghost, so also are understanding, counsel, piety, fortitude, and fear, as stated above (Question 68, Article 4). Therefore these also ought to be placed amongst the gratuitous gifts.
On the contrary, The Apostle says (1 Corinthians 12:8-10): "To one indeed by the Spirit is given the word of wisdom; and to another the word of knowledge, according to the same Spirit; to another, the working of miracles; to another, prophecy; to another, the discerning of spirits; to another divers kinds of tongues; to another interpretation of speeches."
I answer that, As was said above (Article 1), gratuitous grace is ordained to this, viz. that a man may help another to be led to God. Now no man can help in this by moving interiorly (for this belongs to God alone), but only exteriorly by teaching or persuading. Hence gratuitous grace embraces whatever a man needs in order to instruct another in Divine things which are above reason. Now for this three things are required: first, a man must possess the fullness of knowledge of Divine things, so as to be capable of teaching others. Secondly, he must be able to confirm or prove what he says, otherwise his words would have no weight. Thirdly, he must be capable of fittingly presenting to his hearers what he knows.
Now as regards the first, three things are necessary, as may be seen in human teaching. For whoever would teach another in any science must first be certain of the principles of the science, and with regard to this there is "faith," which is certitude of invisible things, the principles of Catholic doctrine. Secondly, it behooves the teacher to know the principal conclusions of the science, and hence we have the word of "wisdom," which is the knowledge of Divine things. Thirdly, he ought to abound with examples and a knowledge of effects, whereby at times he needs to manifest causes; and thus we have the word of "knowledge," which is the knowledge of human things, since "the invisible things of Him... are clearly seen, being understood by the things that are made" (Romans 1:20).
Now the confirmation of such things as are within reason rests upon arguments; but the confirmation of what is above reason rests on what is proper to the Divine power, and this in two ways: first, when the teacher of sacred doctrine does what God alone can do, in miraculous deeds, whether with respect to bodily health--and thus there is the "grace of healing," or merely for the purpose of manifesting the Divine power; for instance, that the sun should stand still or darken, or that the sea should be divided--and thus there is the "working of miracles." Secondly, when he can manifest what God alone can know, and these are either future contingents--and thus there is "prophecy," or also the secrets of hearts--and thus there is the "discerning of spirits."
But the capability of speaking can regard either the idiom in which a person can be understood, and thus there is "kinds of tongues"; or it can regard the sense of what is said, and thus there is the "interpretation of speeches."
Reply to Objection 1. As stated above (Article 1), not all the benefits divinely conferred upon us are called gratuitous graces, but only those that surpass the power of nature--e.g. that a fisherman should be replete with the word of wisdom and of knowledge and the like; and such as these are here set down as gratuitous graces.
Reply to Objection 2. Faith is enumerated here under the gratuitous graces, not as a virtue justifying man in himself, but as implying a super-eminent certitude of faith, whereby a man is fitted for instructing others concerning such things as belong to the faith. With regard to hope and charity, they belong to the appetitive power, according as man is ordained thereby to God.
Reply to Objection 3. The grace of healing is distinguished from the general working of miracles because it has a special reason for inducing one to the faith, since a man is all the more ready to believe when he has received the gift of bodily health through the virtue of faith. So, too, to speak with divers tongues and to interpret speeches have special efficacy in bestowing faith. Hence they are set down as special gratuitous graces.
Reply to Objection 4. Wisdom and knowledge are not numbered among the gratuitous graces in the same way as they are reckoned among the gifts of the Holy Ghost, i.e. inasmuch as man's mind is rendered easily movable by the Holy Ghost to the things of wisdom and knowledge; for thus they are gifts of the Holy Ghost, as stated above (68, A1,4). But they are numbered amongst the gratuitous graces, inasmuch as they imply such a fullness of knowledge and wisdom that a man may not merely think aright of Divine things, but may instruct others and overpower adversaries. Hence it is significant that it is the "word" of wisdom and the "word" of knowledge that are placed in the gratuitous graces, since, as Augustine says (De Trin. xiv, 1), "It is one thing merely to know what a man must believe in order to reach everlasting life, and another thing to know how this may benefit the godly and may be defended against the ungodly."
Source: Summa Theologica (New Advent)