Objection 1. It would seem that knowledge is not a gift. For the gifts of the Holy Ghost surpass the natural faculty. But knowledge implies an effect of natural reason: for the Philosopher says (Poster. i, 2) that a "demonstration is a syllogism which produces knowledge." Therefore knowledge is not a gift of the Holy Ghost.
Objection 2. Further, the gifts of the Holy Ghost are common to all holy persons, as stated above (8, 4; I-II, 68, 5). Now Augustine says (De Trin. xiv, 1) that "many of the faithful lack knowledge though they have faith." Therefore knowledge is not a gift.
Objection 3. Further, the gifts are more perfect than the virtues, as stated above (I-II, 68, 8). Therefore one gift suffices for the perfection of one virtue. Now the gift of understanding responds to the virtue of faith, as stated above (Question 8, Article 2). Therefore the gift of knowledge does not respond to that virtue, nor does it appear to which other virtue it can respond. Since, then, the gifts are perfections of virtues, as stated above (I-II, 68, 1,2), it seems that knowledge is not a gift.
On the contrary, Knowledge is reckoned among the seven gifts (Isaiah 11:2).
I answer that, Grace is more perfect than nature, and, therefore, does not fail in those things wherein man can be perfected by nature. Now, when a man, by his natural reason, assents by his intellect to some truth, he is perfected in two ways in respect of that truth: first, because he grasps it; secondly, because he forms a sure judgment on it.
Accordingly, two things are requisite in order that the human intellect may perfectly assent to the truth of the faith: one of these is that he should have a sound grasp of the things that are proposed to be believed, and this pertains to the gift of understanding, as stated above (Question 8, Article 6): while the other is that he should have a sure and right judgment on them, so as to discern what is to be believed, from what is not to be believed, and for this the gift of knowledge is required.
Reply to Objection 1. Certitude of knowledge varies in various natures, according to the various conditions of each nature. Because man forms a sure judgment about a truth by the discursive process of his reason: and so human knowledge is acquired by means of demonstrative reasoning. On the other hand, in God, there is a sure judgment of truth, without any discursive process, by simple intuition, as was stated in I, 14, 7; wherefore God's knowledge is not discursive, or argumentative, but absolute and simple, to which that knowledge is likened which is a gift of the Holy Ghost, since it is a participated likeness thereof.
Reply to Objection 2. A twofold knowledge may be had about matters of belief. One is the knowledge of what one ought to believe by discerning things to be believed from things not to be believe: in this way knowledge is a gift and is common to all holy persons. The other is a knowledge about matters of belief, whereby one knows not only what one ought to believe, but also how to make the faith known, how to induce others to believe, and confute those who deny the faith. This knowledge is numbered among the gratuitous graces, which are not given to all, but to some. Hence Augustine, after the words quoted, adds: "It is one thing for a man merely to know what he ought to believe, and another to know how to dispense what he believes to the godly, and to defend it against the ungodly."
Reply to Objection 3. The gifts are more perfect than the moral and intellectual virtues; but they are not more perfect than the theological virtues; rather are all the gifts ordained to the perfection of the theological virtues, as to their end. Hence it is not unreasonable if several gifts are ordained to one theological virtue.
Source: Summa Theologica (New Advent)