In the whole question of predestination, Augustine's controversy with the Pelagians occupies the pivotal role, not only because of his influence, but also because during it Augustine was the first church father to overthrow through his reading of Paul the previous theodicy based on free-will which had held the field since Irenaeus. In short it was a genunine theological novum, one proposed to the church catholic on the basis of a new reading of Paul, accepted in the mostly younger churches of the West, and yet rejected by the Greeks who at that time composed the great majority of Christians. As such it is of interest both in terms of content and in terms of the study of theological change. But it is very hard to find, at least on the web, accessible translations of what Augustine actually said about predestination.
Lately I have been reading the excerpts from Augustine on the Epistles of Paul compiled by the English monk, Bede the Venerable (c. 673-735). Bede's work conveniently assembles Augustine's exegetical comments in order, thus enabling his medieval readers (and now us too) to find at a glance what (if any thing) Augustine wrote about any given passage of Paul without searching through the many volumes of his completed works. As the introduction says, Bede's Excerpts was a very influential collection in the Middle Ages, and apart from the clunky and off-putting use of gender-neutral terminology (e.g. "What are human beings that you are mindful of them . . ." etc., p. 337) the translator has done an great service in putting this into English. By translating this anthology, David Hurst not only enables us to see what Augustine said, but also enables us to see exactly what parts of Augustine were influential in the medieval church, which is (need I say it?) the context out of which the Reformation emerged.
Here I reproduce Bede's selection of what Augustine wrote on the famous passage of Romans 9:13-24, the crux of predestination (pp. 84-87):
We must thoroughly examine the Apostle's purpose as to why, in order to emphasize grace, [God] did not choose that the one of whom it was said Jacob I loved, should glory except in the Lord [Mal. 1:3, 1 Co. 1:31]. [Jacob and Esau] were from the same father and the same mother, by one act of intercourse - - and before they had done anything good or evil, God loved the one and hated the other. This was so that Jacob would realize that he was from the lump of original iniquity when he saw that his brother, with whom he had a common origin, in justice deserved to be condemned, and that he could be distinguished only through grace. For, [Paul] says, even before they were born or had done anything good or bad -- in order that God's purpose of election might continue, not by works but by His call -- [Rebecca] was told, 'The elder shall serve the younger.'
The same apostle also clearly asserts in another passage that the election brought about by grace comes from no antecedent merits proceeding from works: 'So too at this time a remnant has been saved through the election of grace. But if by grace, it is no longer because of works; otherwise grace is no longer grace' [Rm. 11:5-6]. Going on, he appropriates the prophet's testimony concerning this grace: As it written, 'Jacob have I loved but Esau I hated,' and then What then are we to say? Is there injustice on God's part? By no means!
Why [did he say] By no means? Was it because He foresaw the future works of both [Esau and Jacob?] Again by no means! For He says to Moses, 'I will show mercy to whom I will show mercy, and have pity on whom I will have pity. So it depends not on the one who wills or runs, but on God, who shows mercy.
--From a letter to the priest Sextus concerning the Pelagians.
If you paid careful attention, you would not extol the merits of the will against grace when you hear that it depends not on the one who wills or runs, but on God, who shows mercy. Therefore God did not show mercy because Jacob willed and ran, but Jacob willed and ran because God showed mercy. 'The will is prepared by the Lord,' and 'A person's steps are directed by the Lord, and He will choose his way' [Ps. 8:35 LXX; Ps. 37:23].
Then because the general statement, It depends not on the one who wills or runs, but on God, Who shows mercy, was made on account of Jacob, he also gives the example of Pharaoh, on account of the words, 'But Esay I hated.' [Paul] adds, For Scripture says to Pharaoh, 'This is why I have raised you up, to show My power through you, and that My name may be proclaimed throughout the earth.' After this, he sums up both: Consequently He shows mercy to whom He wills, and hardens whom He wills. Surely, however, he shows mercy in accordance with grace, which is given freely and not in return for merits, whereas he hardens in accord with a judgment which is in return for merits. To make from a condemned lump a vessel for honorable use is a manifestation of grace, while to make from it a vessel for ignoble use is a just judgment [Rm 9:2; 2 Tm. 2:20].
--From Against Julian 1
[Paul] said, It depends not on the one who wills or runs, but on God, Who shows mercy, not, 'It depends not on the one who wills or scorns, but on God, who hardens.' Hence, since further on he sets down both [ideas] -- Consequently He shows mercy to whom He wills, and He hardens whom He wills -- we are given to understand an agreement with the former statement, so that God's hardness is an unwillingness to show mercy. Thus [God] is not imposing something to make a person worse, but only not imposing something to make a person better.
If [God] makes no distinction in merits, who would not burst out with the words that the Apostle put to himself: You say to me, then, 'Why does He still find fault? For who can oppose His will?' God frequently finds fault with humans -- countless passages in the Scriptures show this - - because they are unwilling to believe and to live upright lives. Hence those who are faithful, and who do his will, are said to live faultless lives since Scripture finds no fault in them. Why does He still find fault? you ask. Who can oppose His will when He shows mercy to whom He wills, and He hardens whom He wills.
The Apostle dulls the brazenness of the question as follows: Who are you, O human, to talk back to God? A person talks back to God when displeased because because God finds fault with sinners -- as if God compels anyone to sin! [God] compels no one to sin, but merely does not bestow the mercy of His righteousness on certain sinners. He is said to harden certain sinners because He does not show them mercy, not because He forces them to sin. He does not show mercy to those to whom -- by His most secret impartiality, which is far beyond human comprehension -- He judges that mercy is not to be granted.
And if you are disturbed because no one resists His will -- since He assists whom He will, and abandons whom He wills, when both the one He assists and the one He abandons are from the same lump of sinners -- and although each deserves punishment, it is taken from one and given to the other -- if you are disturbed, Who are you, O human, to talk back to God? I think human has here the same significant as when he asks, 'Are you not carnal and behaving in a purely human way?' [1 Co. 3:3].
--from To Simplicius, Bishop
Does what is formed say to the one who formed it, 'Why did you make me thus?' Does not the potter have power over the clay, to make from the same lump one vessel for honor and another for shame?
When the entire lump has been rightly condemned, justice pays it deserved shame, and grace gives it undeserved honor. This is not a sign of merit, not as required by fate, not by accident of fortune, but because of the depth of the riches of the wisdom and knowledge of God. The Apostle does not explain it, but marvels at it unexplained, crying out, 'O the depth of the riches of the wisdom and knowledge of God! How unfathomable are His judgments and unsearchable His ways!'
--from the letter cited above to Sixtus, the priest
If God, wishing to show His wrath and demonstrate His power, produced with much patience vessels of wrath fit for destruction -- supply the words, Who are you, to talk back to God? Connecting this statement with the earlier one, then, this must be the meaning: If God, wishing to show His wrath, produced vessels of wrath, who are you to talk back to God?
And not only wishing to show his power, but also what follows, to make known the riches of His glory to the vessels of mercy which He has prepared for glory. What advantage is it for the vessels of completed for destruction that God endures them patiently, so as regularly to annihilate them, and use them for the salvation of those to whom He shows mercy? But surely it is to the advantage of those whose salvation He uses this means, as it is written, 'Let the righteous wash their hands in the blood of sinners!' [Ps. 58:10] -- in other words, let them be cleansed of evil deeds by fear of God when they see the punishment of sinners.
Even us, whom he has called, not only from the Jews, but also from the Gentiles. From Adam comes one lump of sinners and ungodly persons, in which [Jews] and Gentiles, without God's grace, belong to the one dough
--from To Simplician, Bishop, cited above.
To mercy, given freely and not as an obligation, belongs the preparation of vessels for glory and not as an obligation, belongs the preparation of vessels for glory out of the condemned lump, not only from the Jews, as [Paul] says, but also from the Gentiles. For this reason he sets down the testimony of the prophet Hosea, I called those who were not my people 'my people,' and of Isaiah, Concerning Israel, a remnant will be saved.
-- from Against Julian 1
As far as I can tell, Augustine (and Bede) here gives us all of the basic points of Calvinist predestination, without any of the qualification either of Luther's, emphasizing the universal atonement of the incarnate God, or of the Formula of Concord, separating the predestination of the elect from the (non) predestination of those who refuse salvation. Like the more moderate Calvinists, he treats reprobation as reprobation in mass, only election being particular. Likewise he stresses that God's hardening is only His refusal to give (unmerited) grace, and thus is just. But it would seem a just inference from writings to say that as for the lost, God never had any intention of mercy toward them.
So how did Augustine deal with the contrary passages that emphasized God's universal salvific will? Here is Augustine's reading of 1 Timothy 2:4 (pp. 304-05):
Almighty God, whether through the mercy 'He shows to whom He wills,' or the judgment by which 'He hardens whom He wills' [Rm 9:18; Ps. 135:6] does nothing unjustly, nor does He do anything except what He wills, and 'whatever He wills He does.' Therefore because we hear and read in the sacred books that He wills that everyone be saved, although it is certain that not everyone is saved, yet we must not set any limits to the will of the supremely mighty God. Instead we must understand what is written, Who wills that everyone be saved, as saying that no one is saved unless [God] wills it to happen. Not that there is not ["not" missing in Hurst]* a human being whom [God] does not will to be saved, but that no one is saved unless God wills it. Therefore we must ask Him to will it, because what He wills must take place. The Apostle had praying to God in mind when he said this. That is how we understand the words in the Gospel, 'Who enlightens everyone' [Jn 1:9] - - not that anyone is not enlightened, but that no one is enlightened except by Him.
Who wills that everyone be saved was not said because there is no one [Hurst: anyone]* whose salvation He does not will - - He was unwiling to do miraculous deeds among those He said would repent if He did so [Mt. 11:21] - - but because we are to interpret everyone as the whole human race in all its variations. The Apostle had charged that prayers be said for everyone, and especially added for kings and all who are in high positions, whom we may suppose to shrink from the humility of the Christian faith through disdain and worldly pride. Then as he said, This is good in the sight of God our Savior [1 Tm. 2:2,3] - - that is, that we pray on behalf of such as these - - he added at once, to take away despair, who wills that everyone be saved and come to a knowledge of the truth. God, then, has judged this to be good, that by the prayers of the humble he would deign to grant salvation to the lofty - - something we surely have already seen fulfilled.
--from the Enchiridion.
Despite the equivocation, Augustine was clearly uncomfortable with letting the passage simply stand as it would naturally read, that God does indeed desire all to be saved, and gave two possible "interpretations" of it: simply stating that salvation for the elect is purely by God's will (thus recruiting this passage against free will) or else by the argument Calvin later adopted which is that "everyone" here means all classes of people, and adding the twist that it means especially even the proud, who are saved by the prayers of the humble.
*Hurst's translation in these two spots appears to be incorrect (unless Bede has a variant text). Eric Phillips has found the original Latin for these sentences as: "...non quod nullus sit hominum nisi quem salvum fieri velit, sed quod nullus fiat nisi quem velit..." and "...non quod nullus hominum esset quem salvum fieri nollet ...". Thank you, Eric!