(Augustine, On Faith, Hope, & Charity, as provided in Fathers of the Church, Volume 2, p. 447)
The Reformed doctrine of grace, because it is drawn from Scripture, finds resonance in the voice of Augustine, whose love of Scripture lead him to continually study it throughout his life and rely on it as his authority in all matters of doctrine and morals.
Augustine, in the epigraphic quote, does not mention the word "grace" but instead "unmerited mercy." That is simply an equivalent expression. Grace is unmerited favor from God, with the absence of merit being absolutely definitional to the term grace. While this is well recognized in Reformed theology, it is disputed by the theology of Rome.
The following is "Rome's position" (footnote 1) regarding merit:
427. What are the goods that we can merit?- Compendium of the Catechism of the Catholic Church, Question 427 (associated with items 2010-11 and 2027 of the CCC)(emphasis in original)(footnote 2)
Moved by the Holy Spirit, we can merit for ourselves and for others the graces needed for our sanctification and for the attainment of eternal life. Even temporal goods, suitable for us, can be merited in accordance with the plan of God. No one, however, can merit the initial grace which is at the origin of conversion and justification.
The following is one (footnote 3) of Augustine's comments on grace:
And first of all we must be persuaded how much God has loved us, lest through despair we should not dare to be lifted up to Him. But we needed to be shown what kind of men we were whom He loved, lest being proud as it were of our own merits, we should draw away the more from Him, and fail the more in our own strength. And, therefore, God acted towards us in such a way that we might rather profit by His strength, and so the virtue of charity would be perfected in the weakness of humility. He reveals this in the Psalm, where it is said: "Setting aside, O God, a free rain for thy inheritance, and it was weakened, but thou hast made it perfect."[Ps. 67:10?] By the free rain he would have us understand nothing else but grace, which was bestowed not on account of our merits but given freely, and for this reason it is called grace. For He have it not because we were worthy, but because He willed it. If we realize this we shall not trust in ourselves, and this is to be made weak. But He Himself perfects us, who also said to the Apostle Paul: "My grace is sufficient for thee, for strength is made perfect in weakness."[2 Corinthians 12:9] Man had to be persuaded, therefore, how much God loved us, and what kind of men we were whom He loved: how much, that we might not despair, and what kind, that we might not become proud.- Augustine, On the Trinity, Book 4, Chapter 1, Section 2 (taken from the translation in volume 45 of the Fathers of the Church series)
Notice the key portion of this quotation "By the free rain he would have us understand nothing else but grace, which was bestowed not on account of our merits but given freely, and for this reason it is called grace."
Here's an alternative translation, notice what is missing:
We must be persuaded how much God loved us so that we don’t shrink from Him in despair. And we need to be shown also what kind of people we are whom He loved so that we also don’t withdraw from Him out of pride. But He dealt with us so that we could profit from His strength, and, in the weakness of humility, our holiness could be perfected.- Day by Day with the Early Church Fathers, edited by Hudson et al. (presented as transcribed here)
One of the Psalms implies this. It says, “Thou, O God, didst send a spontaneous rain, whereby Thou didst make Thine inheritance perfect, when it was weary.” The “spontaneous rain” is grace given freely and not according to merit. He didn’t give it because we were worthy, but because He willed. Knowing this, we shouldn’t trust in ourselves. That is what is meant by being made “weak.”
However, He perfects us and says to the Apostle Paul, “My grace is sufficient for thee, for my strength is made perfect in weakness.” We, then, must be persuaded how much God loved us and what type of people we were whom He loved. The former is important, lest we despair; the latter, lest we become proud.
The Schaff collection's translation has a slightly different wording:
And first we have had to be persuaded how much God loved us, lest from despair we should not dare to look up to Him. And we needed to be shown also what manner of men we are whom He loved, lest being proud, as if of our own merits, we should recede the more from Him, and fail the more in our own strength. And hence He so dealt with us, that we might the rather profit by His strength, and that so in the weakness of humility the virtue of charity might be perfected. And this is intimated in the Psalm, where it is said, “Thou, O God, didst send a spontaneous rain, whereby Thou didst make Thine inheritance perfect, when it was weary.” [Ps. lxviii. 9.—Pluviam voluntariam.] For by “spontaneous rain” nothing else is meant than grace, not rendered to merit, but given freely, [Gratis.] whence also it is called grace; for He gave it, not because we were worthy, but because He willed. And knowing this, we shall not trust in ourselves; and this is to be made “weak.” But He Himself makes us perfect, who says also to the Apostle Paul, “My grace is sufficient for thee, for my strength is made perfect in weakness.” [2 Cor. xii. 9] Man, then, was to be persuaded how much God loved us, and what manner of men we were whom He loved; the former, lest we should despair; the latter, lest we should be proud.- Augustine, On the Trinity, Book 4, Chapter 1, Section 2 (taken from the translation in NPNF1-03)(footnotes presented within brackets) Essentially the same translation may be found in The Works of Aurelius Augustine, a New Translation, Volume 7 (link)
Notice, however, that while this is a different wording, it is the same concept: "For by “spontaneous rain” nothing else is meant than grace, not rendered to merit, but given freely, whence also it is called grace; for He gave it, not because we were worthy, but because He willed."
This is not an isolated instance of this definition of grace for Augustine, he says much the same thing in his work, On Grace and Free Will:
When God says, “Turn ye unto me, and I will turn unto you,” [Zech. i. 3.] one of these clauses—that which invites our return to God—evidently belongs to our will; while the other, which promises His return to us, belongs to His grace. Here, possibly, the Pelagians think they have a justification for their opinion which they so prominently advance, that God’s grace is given according to our merits. In the East, indeed, that is to say, in the province of Palestine, in which is the city of Jerusalem, Pelagius, when examined in person by the bishop, [See On the Proceedings of Pelagius, above, ch. xiv. (30–37).] did not venture to affirm this. For it happened that among the objections which were brought up against him, this in particular was objected, that he maintained that the grace of God was given according to our merits,—an opinion which was so diverse from catholic doctrine, and so hostile to the grace of Christ, that unless he had anathematized it, as laid to his charge, he himself must have been anathematized on its account. He pronounced, indeed, the required anathema upon the dogma, but how insincerely his later books plainly show; for in them he maintains absolutely no other opinion than that the grace of God is given according to our merits. Such passages do they collect out of the Scriptures,—like the one which I just now quoted, “Turn ye unto me, and I will turn unto you,”—as if it were owing to the merit of our turning to God that His grace were given us, wherein He Himself even turns unto us. Now the persons who hold this opinion fail to observe that, unless our turning to God were itself God’s gift, it would not be said to Him in prayer, “Turn us again, O God of hosts;” [Ps. lxxx. 7.] and, “Thou, O God, wilt turn and quicken us;” [Ps. lxxxv. 6.] and again, “Turn us, O God of our salvation,” [Ps. lxxxv. 4.] —with other passages of similar import, too numerous to mention here. For, with respect to our coming unto Christ, what else does it mean than our being turned to Him by believing? And yet He says: “No man can come unto me, except it were given unto him of my Father.” [John vi. 65.]- Augustine, On Grace and Free Will, Chapter 10 (Section V in the Latin)(footnotes placed into brackets)
Notice that Augustine places essentially the Roman view in the mouth of Pelagius: "God’s grace is given according to our merits."
Here surely is at fault the vain reasoning of those who defend the foreknowledge of God in opposition to His grace, and with this view declare that we were chosen before the foundation of the world, [Eph. i. 4.] because God foreknew that we should be good, but not that He Himself would make us good. So says not He, who declares, “Ye have not chosen me.” For had He chosen us on the ground that He foreknew that we should be good, then would He also have foreknown that we would not be the first to make choice of Him. For in no other way could we possibly be good: unless, forsooth, one could be called good who has never made good his choice. What was it then that He chose in those who were not good? For they were not chosen because of their goodness, inasmuch as they could not be good without being chosen. Otherwise grace is no more grace, if we maintain the priority of merit. Such, certainly, is the election of grace, whereof the apostle says: “Even so then at this present time also there is a remnant saved according to the election of grace.” To which he adds: “And if by grace, then is it no more of works; otherwise grace is no more grace.” [Rom. xi. 5, 6.] Listen, thou ungrateful one, listen: “Ye have not chosen me, but I have chosen you.” Not that thou mayest say, I am chosen because I already believed. For if thou wert believing in Him, then hadst thou already chosen Him. But listen: “Ye have not chosen me.” Not that thou mayest say, Before I believed I was already doing good works, and therefore was I chosen. For what good work can be prior to faith, when the apostle says, “Whatsoever is not of faith is sin”? [Rom. xiv. 23.] What, then, are we to say on hearing such words, “Ye have not chosen me,” but that we were evil, and were chosen in order that we might be good through the grace of Him who chose us? For it is not by grace, if merit preceded: but it is of grace: and therefore that grace did not find, but effected the merit.- Augustine, Tractate 86 on the Gospel of John, Section 2 (footnotes placed in brackets)
The key sentence in the above quotation is: "Otherwise grace is no more grace, if we maintain the priority of merit." Rome's view, which permits grace to be on the priority of merit calls something grace that is not grace.
And yet again:
He commendeth the grace whereby He calleth according to His own purpose. Of which purpose the apostle says, “We know that all things work together for good to them that love God, to those who are called according to the purpose of God,” [Rom. viii. 28.] to wit, the purpose of Him that calleth, not of those who are called; which is put still more clearly in another place in this way, “Labor together in the gospel according to the power of God, who saveth us and calleth us with His holy calling, not according to our works, but according to His own purpose and grace.” [2 Tim. i. 8, 9.] For if our thoughts turn to the nature wherein we have been created, inasmuch as we were all created by the Truth, who is there that is not of the truth? But it is not all to whom it is given of the truth to hear, that is, to obey the truth, and to believe in the truth; while in no case certainly is there any preceding of merit, lest grace should cease to be grace. For had He said, Every one that heareth my voice is of the truth, then it would be supposed that he was declared to be of the truth because he conforms to the truth; it is not this, however, that He says, but, “Every one that is of the truth heareth my voice.” And in this way he is not of the truth simply because he heareth His voice; but only on this account he heareth, because he is of the truth, that is, because this is a gift bestowed on him of the truth. And what else is this, but that by Christ’s gracious bestowal he believeth on Christ?- Augustine, Tractate 115 on the Gospel of John, Section 4 (footnotes placed in brackets)
In the above quotation, we see the similar expression: "while in no case certainly is there any preceding of merit, lest grace should cease to be grace."
Now this election the Apostle demonstrating to be, not of merits going before in good works, but election of grace, saith thus: “And in this time a remnant by election of grace is saved. But if by grace, then is it no more of works, otherwise grace is no more grace.” [Rom. xi. 5, 6] This is election of grace; that is, election in which through the grace of God men are elected: this, I say, is election of grace which goes before all good merits of men. For if it be to any good merits that it is given, then is it no more gratuitously given, but is paid as a debt, and consequently is not truly called grace; where “reward,” as the same Apostle saith, “is not imputed as grace, but as debt.” [Rom. iv. 4] Whereas if, that it may be true grace, that is, gratuitous, it find nothing in man to which it is due of merit, (which thing is well understood in that saying, “Thou wilt save them for nothing,” [Psalm lvi. 7, Lat. and LXX. ὑπšρ τοῦ μηθενὸς σὡσεις αὐτούς. But Heb. and E.V. “shall they escape by iniquity?”]) then assuredly itself gives the merits, not to merits is given. Consequently it goes before even faith, from which it is that all good works begin. “For the just,” as is written, “shall live by faith.” [Habak. ii. 4] But, moreover, grace not only assists the just, but also justifies the ungodly. And therefore even when it does aid the just and seems to be rendered to his merits, not even then does it cease to be grace, because that which it aids it did itself bestow. With a view therefore to this grace, which precedes all good merits of man, not only was Christ put to death by the ungodly, but “died for the ungodly.” [Rom. v. 6] And ere that He died, He elected the Apostles, not of course then just, but to be justified: to whom He saith, “I have chosen you out of the world.” For to whom He said, “Ye are not of the world,” and then, lest they should account themselves never to have been of the world, presently added, “But I have chosen you out of the world;” assuredly that they should not be of the world was by His own election of them conferred upon them. Wherefore, if it had been through their own righteousness, not through His grace, that they were elected, they would not have been chosen out of the world, because they would already not be of the world if already they were just. And again, if the reason why they were elected was, that they were already just, they had already first chosen the Lord. For who can be righteous but by choosing righteousness? “But the end of the law is Christ, for righteousness is to every one that believeth. [Rom. x. 4] Who is made unto us wisdom of God, and righteousness, and sanctification, and redemption: that, as it is written, He that glorieth, let him glory in the Lord.” [1 Cor. i. 30, 31] He then is Himself our righteousness.- Augustine, On Patience, Section 17 (footnotes placed in brackets)
Again note Augustine's explanation: "For if it be to any good merits that it is given, then is it no more gratuitously given, but is paid as a debt, and consequently is not truly called grace ... ."
Read with a little more attention its exposition in the treatise of the blessed martyr Cyprian, which he wrote concerning this matter, the title of which is, On the Lord’s Prayer; and see how many years ago, and what sort of an antidote was prepared against those poisons which the Pelagians were one day to use. For there are three points, as you know, which the catholic Church chiefly maintains against them. One of these is, that the grace of God is not given according to our merits; because even every one of the merits of the righteous is God’s gift, and is conferred by God’s grace. The second is, that no one lives in this corruptible body, however righteous he may be, without sins of some kind. The third is, that man is born obnoxious to the first man’s sin, and bound by the chain of condemnation, unless the guilt which is contracted by generation be loosed by regeneration. Of these three points, that which I have placed last is the only one that is not treated of in the above-named book of the glorious martyr; but of the two others the discourse there is of such perspicuity, that the above-named heretics, modern enemies of the grace of Christ, are found to have been convicted long before they were born. Among these merits of the saints, then, which are no merits unless they are the gifts of God, he says that perseverance also is God’s gift, in these words: “We say, ‘Hallowed be Thy name;’ not that we ask for God that He may be hallowed by our prayers, but that we beseech of Him that His name may be hallowed in us. But by whom is God sanctified, since He Himself sanctifies? Well, because He says, Be ye holy because I also am holy, we ask and entreat that we, who were sanctified in baptism, may persevere in that which we have begun to be.” [Cyprian, On the Lord’s Prayer; see The Ante-Nicene Fathers, vol. v. p. 450.] And a little after, still arguing about that self-same matter, and teaching that we entreat perseverance from the Lord, which we could in no wise rightly and truly do unless it were His gift, he says: “We pray that this sanctification may abide in us; and because our Lord and Judge warns the man that was healed and quickened by Him to sin no more, lest a worse thing happen unto him, we make this supplication in our constant prayers; we ask this, day and night, that the sanctification and quickening which is received from the grace of God may be preserved by His protection.” [Cyprian, On the Lord’s Prayer, as above.] That teacher, therefore, understands that we are asking from Him for perseverance in sanctification, that is, that we should persevere in sanctification, when we who are sanctified say, “Hallowed be Thy name.” For what else is it to ask for what we have already received, than that it be given to us also not to cease from its possession? As, therefore, the saint, when he asks God that he may be holy, is certainly asking that he may continue to be holy, so certainly the chaste person also, when he asks that he may be chaste, the continent that he may be continent, the righteous that he may be righteous, the pious that he may be pious, and the like,—which things, against the Pelagians, we maintain to be God’s gifts,—are asking, without doubt, that they may persevere in those good things which they have acknowledged that they have received. And if they receive this, assuredly they also receive perseverance itself, the great gift of God, whereby His other gifts are preserved.- Augustine, On the Predestination of the Saints, Chapter 4 (Section II in the Latin)(footnotes placed in brackets)
Notice how in the above quotation, Augustine speaks exactly contrary to the Roman catechism. He declares that "perseverance in sanctification" is gracious and (consequently) not on account of merit. I don't expect anyone to agree with Augustine's definition of grace, simply because Augustine said it. Read Scripture (as Augustine would have wanted you to do) and see for yourself whether Augustine or the Roman Catholic Church is right about this issue.
Augustine tells us where he gets his ideas about grace: "From these and similar passages of Scripture, we gather the proof that God's grace is not given according to our merits." (Augustine, On Grace and Free Will, Chapter 13, (Section 6 in the Latin)) So, search the Scriptures and see whether these things be as we have told you. Scripture is what proved it to us and to Augustine, perhaps it will prove it to you as well, dear reader, if you do not already agree.
Footnote 1: "Official" in the sense of being a public teaching in an official document. The document itself, however, like the overwhelming majority of documents in Catholicism, does not purport to be infallible.
Footnote 2: Note that this compendium serves to explain how simultaneously Rome claims: "Our justification comes from the grace of God. Grace is favor, the free and undeserved help that God gives us to respond to his call to become children of God, adoptive sons, partakers of the divine nature and of eternal life." (CCC1996) If that statement were taken by itself, Rome would sound nearly orthodox in its theology of grace. The fact of the matter, however, is that such a definition is applied exclusively to what Rome calls "initial grace."
Footnote 3: Augustine's works are massive and imposing. I don't make this blog post out to be the last scholarly word on the subject. Perhaps I've missed something in my reading of Augustine that ends up undoing the force of the material he provides here.