If Calvin got his theology from Augustine, he seriously misunderstood him: "If, however, being
already regenerate and justified, he relapses of his own will into an evil life,
assuredly he cannot say, I have not received, because of his own free choice to evil
he has lost the grace of God, that he had received.—Augustine,
On Rebuke and Grace, c. AD 426 or 427, Chapter 9)
https://www.newadvent.org/fathers/1513.htm
continued:
Chapter 14.— None of the Elect and Predestinated Can Perish.
Of such says the apostle, We
know that to those that
love God He works together all things for good, to them who are called according to His purpose; because those whom He before foreknew, He also did
predestinate to be conformed to the image of His Son, that He might be the
first-born among many brethren. Moreover, whom He did
predestinate, them He also called; and whom He called, them He also justified; and whom He justified, them He also
glorified. Of these no one perishes, because all are elected. And they are elected because they were called according to the purpose — the purpose, however, not their own, but God's; of which He elsewhere says, That the purpose of God according to election might stand, not of works, but of Him that calls, it was said to her that the elder shall serve the younger.
Romans 9:11 And in another place he says, Not according to our works, but according to His own purpose and
grace.
2 Timothy 1:9 When, therefore, we hear, Moreover, whom He did
predestinate, them He also called,
Romans 8:29 we ought to acknowledge that they were called according to His purpose; since He thence began, saying, He works together all things for good to those who are called according to His purpose, and then added, Because those whom He before foreknew, He also did
predestinate, to be conformed to the image of His Son, that He might be the
first-born among many brethren. And to these promises He added, Moreover, whom He did
predestinate, them He also called. He wishes these, therefore, to be understood whom He called according to His purpose, lest any among them should be thought to be called and not elected, on account of that sentence of the Lord's: Many the called but few are elected.
Matthew 20:16 For whoever are elected are without
doubt also called; but not whosoever are called are as a consequence elected. Those, then, are elected, as has often been said, who are called according to the purpose, who also are
predestinated and foreknown. If any one of these perishes, God is mistaken; but none of them perishes, because God is not mistaken. If any one of these perish, God is overcome by
human sin; but none of them perishes, because God is overcome by nothing. Moreover, they are elected to reign with Christ, not as Judas was elected, to a work for which he was fitted. Because he was chosen by Him who well
knew how to make use even of
wicked men, so that even by his damnable deed that venerable work, for the sake of which He Himself had come, might be accomplished. When, therefore, we hear, Have not I chosen you twelve, and one of you is a
devil?
John 6:70 we ought to understand that the rest were elected by mercy, but he by judgment; those to obtain His kingdom, he to shed His blood!
Chapter 15.— Perseverance is Given to the End.
Rightly follows the word to the kingdom of the elect: If God be for us, who can be against us? He that spared not His own Son, but delivered Him up for us all, how has He not also with Him given us all things? Who shall lay anything to the charge of God's elect? God who justifies? Who condemns? Christ who died? Yea, rather who rose again also, who is at the right hand of
God, who also solicits on our behalf? And of how steadfast a perseverance even to the end they have received the gift, let them follow on to say: Who shall separate us from the
love of Christ? Shall tribulation, or distress, or
persecution, or famine, or nakedness, or peril, or sword? As it is written, Because for your sake we are killed all the day long, we are accounted as sheep for the slaughter. But in all these things we are more than conquerors, through Him that has loved us. For I am certain, that neither death, nor life, nor
angel, nor principality, nor things present, nor things to come, nor power, nor height, nor depth, nor any other creature, shall be able to separate us from the
love of God which is in
Christ Jesus our Lord.
Chapter 16.— Whosoever Do Not Persevere are Not Distinguished from the Mass of Perdition by Predestination.
Such as these were they who were signified to Timothy, where, when it had been said that Hymenæus and Philetus had subverted the
faith of some, it is presently added, Nevertheless the foundation of
God stands sure, having this seal, The Lord has
known them that are His.
2 Timothy 2:19 The
faith of these, which works by
love, either actually does not fail at all, or, if there are any whose
faith fails, it is restored before their life is ended, and the iniquity which had intervened is done away, and perseverance even to the end is allotted to them. But they who are not to persevere, and who shall so fall away from
Christian faith and conduct that the end of this life shall find them in that case, beyond all
doubt are not to be reckoned in the number of these, even in that season wherein they are living well and piously. For they are not made to differ from that mass of perdition by the foreknowledge and
predestination of
God, and therefore are not called according to God's purpose, and thus are not elected; but are called among those of whom it was said, Many are called, not among those of whom it was said, But few are elected. And yet who can deny that they are elect, since they
believe and are
baptized, and live according to God? Manifestly, they are called elect by those who are
ignorant of what they shall be, but not by Him who
knew that they would not have the perseverance which leads the elect forward into the blessed life, and
knows that they so stand, as that He has foreknown that they will fall.