Thomas Aquinas

“ Yet in neither way is debt taken to mean that God is under an obligation to His creature, but rather that the creature ought to be subject to God, that the Divine ordination may be fulfilled in it, which is that a certain nature should have certain conditions or properties, and that by doing certain works it should attain to something further. And hence natural endowments are not a debt in the first sense but in the second. Hence they especially merit the name of grace. ”

“ And thus if grace is taken for God's gratuitous motion whereby He moves us to meritorious good, it is fittingly divided into operating and cooperating grace.
But if grace is taken for the habitual gift, then again there is a double effect of grace, even as of every other form; the first of which is "being," and the second, "operation"; thus the work of heat is to make its subject hot, and to give heat outwardly. And thus habitual grace, inasmuch as it heals and justifies the soul, or makes it pleasing to God, is called operating grace ”

“ 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. ”

“ God does not justify us without ourselves, because whilst we are being justified we consent to God's justification [justitiae] by a movement of our free-will. Nevertheless this movement is not the cause of grace, but the effect; hence the whole operation pertains to grace.
Reply to Objection 3: One thing is said to cooperate with another not merely when it is a secondary agent under a principal agent, but when it helps to the end intended. Now man is helped by God to will the good, through the means of operating grace. And hence, the end being already intended, grace cooperates with us. ”

“ 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 ”

“ 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. ”

“ 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. ”

“ 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. ”