Monergistic regeneration means that regeneration is accomplished by a single actor, God. It means literally a “one-working.” [R.C. Sproul: Willing to Believe: The Controversy over Free Will, pages 23]. As indicated in Sproul’s statement, monergism is closely tied to regeneration and this regeneration precedes faith.
The Reformers taught not only that regeneration does precede faith but also it must precede faith. Because of the moral bondage of the unregenerate sinner, he cannot have faith until he is changed internally by the operative, monergistic work of the Holy Spirit. Faith is regeneration’s fruit, not its cause.
R.C. Sproul: Willing to Believe: The Controversy over Free Will, pages 23
How about conversion and sanctification? According to Sproul and Berkhof these two are not monergistic in nature but synergistic.
This view is clearly monergistic at the initial point of the sinner’s movement from unbelief to faith. The whole process, however, is not monergistic. Once the operative grace of regeneration is given, the rest of the process is synergistic. That is, after the soul has been changed by effectual or irresistible grace, the person himself chooses Christ. God does not make the choice for him. It is the person who believes, not God who believes for him. Indeed the rest of the Christian life of sanctification unfolds in a synergistic pattern.
There is much confusion about the debate between monergism and synergism. When Augustinianism is defined as monergistic, one must remember that it is monergistic with respect to the beginning of salvation, not to the whole process. Augustinianism does not reject all synergism, but does reject a synergism that is all synergism.
R.C. Sproul: Willing to Believe: The Controversy over Free Will, pages 73
Regeneration, then, is to be conceived monergistically. God alone works, and the sinner has no part in it whatsoever. This, of course, does not mean, that man does not co-operate in later stages of the work of redemption. It is quite evident from Scripture that he does.
Berkhof, Systematic Theology, page 473
But though God only is the author of conversion, it is of great importance to stress the fact, over against a false passivity, that there is’ also a certain co-operation of man in conversion.
ibid, page 490
We can conclude that according to both Berkhof and Sproul: (1) only regeneration is monergistic in nature; (2) regeneration takes place before (synergistic) conversion and (synergistic) sanctification and (3) regeneration is distinct from conversion and sanctification. Interestingly, according to Berkhof’s investigation this view is a later development, i.e. it comes neither from Luther nor Calvin.
Luther did not entirely escape the confusion of regeneration with justification. Moreover, he spoke of regeneration or the new birth in a rather broad sense. Calvin also used the term in a very comprehensive sense as a designation of the whole process by which man is renewed, including, besides the divine act which originates the new life, also conversion (repentance and faith) and sanctification [Inst. III.3.9]. Several seventeenth century authors fail to distinguish between regeneration and conversion, and use the two terms interchangeably, treating of what we now call regeneration under vocation or effectual calling. The Canons of Dort also use the two words synonymously [III and IV. 11, 12], and the Belgic Confession seems to speak regeneration in an even wider sense [Art. XXIV].
Berkhof, Systematic Theology, page 466
In contrast Sproul concluded that the Reformers (plural, presumably Luther and Calvin) held the same view as he and Berkhof do (refer to his statement at the beginning of this post). According to Berkhof neither did the early Church believe the same view. Yet at the same time he insisted that Augustine adopted monergism in the same way he and Sproul believe.
In the mind of the early Church the term “regeneration” did not stand for a sharply defined concept. It was used to denote a change closely connected with the washing away of sins, and no clear distinction was made between regeneration and justification. As identified with baptismal grace, the former was understood especially as a designation of the remission of sin, though the idea of a certain moral renovation was not excluded. Even Augustine did not draw a sharp line here, but did distinguish between regeneration and conversion. To him regeneration included, in addition to the remission of sin, only an initial change of the heart, followed by conversion later on. He conceived of it as a strictly monergistic work of God, in which the human subject cannot cooperate, and which man cannot resist
Berkhof, Systematic Theology, pages 465-466
Berkhof wrote that Augustine’s regeneration includes remission of sin through baptism – something that neither he nor Sproul believe. He did not provide us the source of Augustine statement either. It is unlikely that Augustine believed in remission of sins (through baptism) as part of regeneration that takes place before conversion, unless he wrote about infant baptism. As pointed out correctly by Berkhof, to Augustine regeneration takes place in (Sacrament of) Baptism – something that is also admitted by Sproul (just like Berkhof, at the same time he also insisted that Augustine taught monergism in the same way present-day Calvinists understand):
It must be noted that here [Council of Orange decrees], as well as in Augustine, the grace of regeneration is effected by the sacrament of baptism. Baptismal regeneration was later rejected categorically by Calvinists as well as most other Protestants.
R.C. Sproul: Willing to Believe: The Controversy over Free Will, pages 76
The fact that Augustine taught baptism of regeneration, which is still the belief of the Catholic Church, is undeniable. In the words of Augustine (underlined emphasis added)
As a consequence, then, of this disobedience of the flesh and this law of sin and death, whoever is born of the flesh has need of spiritual regeneration—not only that he may reach the kingdom of God, but also that he may be freed from the damnation of sin. Hence men are on the one hand born in the flesh liable to sin and death from the first Adam, and on the other hand are born again in baptism associated with the righteousness and eternal life of the second Adam; even as it is written in the book of Ecclesiasticus: “Of the woman came the beginning of sin, and through her we all die.” [Ecclesiasticus or Sirach 25:24]
Augustine, a Treatise on the Merits and Forgiveness of Sins, and on the Baptism of Infants, Book I Chapter 21
If any man, however, is still perplexed by the question why the children of baptized persons are baptized, let him briefly consider this: Inasmuch as the generation of sinful flesh through the one man, Adam, draws into condemnation all who are born of such generation, so the generation of the Spirit of grace through the one man Jesus Christ, draws to the justification of eternal life all who, because predestinated, partake of this regeneration. But the sacrament of baptism is undoubtedly the sacrament of regenation: Wherefore, as the man who has never lived cannot die, and he who has never died cannot rise again, so he who has never been born cannot be born again. From which the conclusion arises, that no one who has not been born could possibly have been born again in his father. Born again, however, a man must be, after he has been born; because, “Except a man be born again, he cannot see the kingdom of God” [John 3:5] Even an infant, therefore, must be imbued with the sacrament of regeneration, lest without it his would be an unhappy exit out of this life; and this baptism is not administered except for the remission of sins. And so much does Christ show us in this very passage; for when asked, How could such things be? He reminded His questioner of what Moses did when he lifted up the serpent. Inasmuch, then, as infants are by the sacrament of baptism conformed to the death of Christ, it must be admitted that they are also freed from the serpent’s poisonous bite, unless we wilfully wander from the rule of the Christian faith. This bite, however, they did not receive in their own actual life, but in him on whom the wound was primarily inflicted.
Augustine, a Treatise on the Merits and Forgiveness of Sins, and on the Baptism of Infants, Book II Chapter 43
Augustine also stated that regeneration that begins in Baptism will be continued through-out our life (here he equates regeneration with renewal) – something that both Berkhof and Sproul (and any Calvinist of today) will reject.
For it is not from the moment of a man’s baptism that all his old infirmity is destroyed, but renovation begins with the remission of all his sins, and so far as he who is now wise is spiritually wise. All things else, however, are accomplished in hope, looking forward to their being also realized in fact, even to the renewal of the body itself in that better state of immortality and incorruption with which we shall be clothed at the resurrection of the dead. For this too the Lord calls a regeneration,—though, of course, not such as occurs through baptism, but still a regeneration wherein that which is now begun in the spirit shall be brought to perfection also in the body. “In the regeneration,” says He, “when the Son of man shall sit in the throne of His glory, ye also shall sit upon twelve thrones, judging the twelve tribes of Israel.” [Matthew 19:28] For however entire and full be the remission of sins in baptism, nevertheless, if there was wrought by it at once, an entire and full change of the man into his everlasting newness,—I do not mean change in his body, which is now most clearly tending evermore to the old corruption and to death, after which it is to be renewed into a total and true newness,—but, the body being excepted, if in the soul itself, which is the inner man, a perfect renewal was wrought in baptism, the apostle would not say: “Even though our outward man perishes, yet the inward man is renewed day by day.” [2 Corinthians 4:16] Now, undoubtedly, he who is still renewed day by day is not as yet wholly renewed; and in so far as he is not yet wholly renewed, he is still in his old state. Since, then, men, even after they are baptized, are still in some degree in their old condition, they are on that account also still children of the world; but inasmuch as they are also admitted into a new state, that is to say, by the full and perfect remission of their sins, and in so far as they are spiritually-minded, and behave correspondingly, they are the children of God. Internally we put off the old man and put on the new; for we then and there lay aside lying, and speak truth, and do those other things wherein the apostle makes to consist the putting off of the old man and the putting on of the new, which after God is created in righteousness and true holiness [Ephesians 4:24]. Now it is men who are already baptized and faithful whom he exhorts to do this,—an exhortation which would be unsuitable to them, if the absolute and perfect change had been already made in their baptism. And yet made it was, since we were then actually saved; for “He saved us by the laver of regeneration.” [Titus 3:5] In another passage, however, he tells us how this took place. “Not they only,” says he, “but ourselves also, which have the first-fruits of the Spirit, even we ourselves groan within ourselves, waiting for the adoption, to wit, the redemption of our body. For we are saved by hope: but hope that is seen is not hope; for what a man seeth, why doth he yet hope for? But if we hope for that we see not, then do we with patience wait for it.” [Romans 8:23-25]
Augustine, a Treatise on the Merits and Forgiveness of Sins, and on the Baptism of Infants, Book II Chapter 9
To conclude since Augustine understanding of regeneration does not match with that of present-day Calvinists (who consider that only regeneration is monergistic in nature), he was not a monergist (and will never be).