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" (Rm. 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."