Gal 3:21-22
21 Is the law then against the promises of God? God forbid: for if there had been a law given which could have given life, verily righteousness should have been by the law.
22 But the scripture hath concluded all under sin, that the promise by faith of Jesus Christ might be given to them that believe.
(KJV)
Likewise, I've never been to a Christian Church that didn't believe we all were concluded under sin, and that so God's Salvation through His Son Jesus Christ would be for those who by Faith believe on Him. Thus I don't see Augustine nor Calvin having been able to modify that concept.
The Biblical concept they did try to modify was the above concept in relation to God's predestination of His elect. The idea of God having chosen His elect before the foundation of the world is what stumped them, and still what stumps many brethren today.
For me what Jesus prayed in John 17 answers the whole matter, even what Apostle Paul said in Rom.9 about God hating Esau but loving Jacob even before either child was yet born or having chance to do good or evil.
John 17:5-21
5 And now, O Father, glorify thou Me with Thine own self with the glory which I had with Thee before the world was.
6 I have manifested Thy name unto the men which Thou gavest Me out of the world: Thine they were, and Thou gavest them Me; and they have kept Thy word.
What is our Lord Jesus saying there? Who are those He revealed that before belonged to The Father, then The Father gave them to Jesus? When our Lord Jesus said "Thine they were", that means previous ownership by The Father. That's going way back in time, even before the foundation of this present world. That's how far back The Father had made His predestination of His elect chosen servants. Jesus is talking about those like His Apostles who were chosen elect.
7 Now they have known that all things whatsoever Thou hast given Me are of Thee.
How did Christ's Apostles know that? Jesus taught them personally, showed them.
8 For I have given unto them the words which Thou gavest Me; and they have received them, and have known surely that I came out from Thee, and they have believed that Thou didst send Me.
Apostle Peter replied to Jesus' question of who He was by saying Jesus is The Christ testified of by the OT prophets.
9 I pray for them: I pray not for the world, but for them which Thou hast given Me; for they are Thine.
10 And all Mine are Thine, and Thine are Mine; and I am glorified in them.
By that our Lord Jesus is declaring His Divine origin with The Father. He declared ownership of The Father's chosen servants along with The Father.
11 And now I am no more in the world, but these are in the world, and I come to Thee. Holy Father, keep through Thine own name those whom Thou hast given Me, that they may be one, as We are.
Again, our Lord Jesus refers to His chosen Apostles that were with Him during His Ministry.
12 While I was with them in the world, I kept them in Thy name: those that Thou gavest Me I have kept, and none of them is lost, but the son of perdition; that the scripture might be fulfilled.
Only one of the Apostles was lost, which was Judas Iscariot who betrayed Jesus to be crucified, which this shows Judas was also chosen for that in order to fulfill the OT prophecy. (Keep in mind that Judas has still yet to be judged and sentenced to perish, for the Judgment day of Rev.20 is still yet to come).
13 And now come I to Thee; and these things I speak in the world, that they might have My joy fulfilled in themselves.
14 I have given them Thy word; and the world hath hated them, because they are not of the world, even as I am not of the world.
15 I pray not that thou shouldest take them out of the world, but that thou shouldest keep them from the evil.
16 They are not of the world, even as I am not of the world.
The world hated our Lord Jesus' Apostles because they are not of the world, even as He is not of this world. What does that mean exactly? It has to be about their spirit in them as influenced by The Holy Spirit, their being already owned by God, even before their birth (like Jacob, Moses, Jeremiah, etc.).
17 Sanctify them through Thy truth: Thy word is truth.
18 As Thou hast sent Me into the world, even so have I also sent them into the world.
The idea of a 'sent' one is where the meaning of the word apostle comes from. It means having been already predestinated in service. Jesus specifically chose Apostle Paul into His service when Paul was deceived and delivering up Christians to be tried by the unbelieving Jews at Jerusalem. Paul (his name Saul back then) even held the coats of those who stoned Christ's servant Stephen. And he had a letter of authority from the Jews while on the way to Damascus to hunt down more Christians, when our Lord Jesus struck him down with blindness and spoke to him personally. Thus Paul was one of the strongest Bible examples of a predestined chosen elect, for Paul did not come to Christ, Christ came to him and removed any doubt as to who Jesus is.
19 And for their sakes I sanctify Myself, that they also might be sanctified through the truth.
Only God can sanctify Himself. Thus our Lord Jesus once again revealed His Divine origin with The Father by that statement, showing He is co-equal with The Father.
20 Neither pray I for these alone, but for them also which shall believe on Me through their word;
This is where those of us who are not... predestined chosen 'sent' elect our Lord Jesus addressed. There He speaks of two groups. The first are those He 'sent' which are chosen, sent, that He and The Father already own. The second group are those He said, "them also which shall believe on Me through their word." That means those who come to Faith on Christ Jesus by their own free will from hearing The Gospel preached by those whom Jesus sent.
By this our Lord Jesus reveals what He meant when He said many are called, but few are chosen. Understanding this should come naturally as bread and butter. God predestinated His chosen sent ones in service to Him prior to their birth, and He already owned them beforehand. That is why we have so many Bible examples of His influencing events in their lives, and keeping them on the straight and narrow when they veer (like Jonah for a huge example), and Paul's thorn in the side to keep him straight.
That does not mean God will not influence events in the lives of those who come to Christ of their own will. He will automatically do it for His elect sent ones He already owns though, controlling events for them even without their having asked Him anything. With us who are not 'sent' ones, we need to ask Him, declare our Faith on Him through His Son.
21 That they all may be one; as Thou, Father, art in Me, and I in Thee, that they also may be one in Us: that the world may believe that Thou hast sent Me.
(KJV)
The result of His 'sent' ones He already owned and chose preaching The Gospel to those who hear and believe by their own free will, is that both groups together, are to become one in Him and The Father. That's an application for His Church as a whole.
The confusion away from the above comes when some try to remove the idea of free will of that second group which hears The Gospel by Christ's chosen sent ones, His sent ones being those He and The Father already own.
The matter on that point is especially about 'ownership'. And if He already owns them, can He influence their hearts and free will? Yes! That is especially who Paul was speaking about in Romans 8 that have already been predestined, called, justified, and glorified. When we as part of that second group of John 17:20 hear The Gospel preached by those He 'sent', and believe on Christ Jesus by Faith, we become joined with His chosen elect in that, as long as we do not fall away from Him.
That's the main difference with that second group of believers that come to Christ using their own free will. Those also have the choice to stray while those 'sent' He already owned beforehand He will directly intervene with so they cannot stray from Him. God's prophet Jonah is a prime example of the latter.
God sent Jonah to preach to the pagan city of Nineveh because those people had fallen into great wickedness and God was preparing to destroy it. Jonah tried to run away. He even cast himself over the side of the ship he was in thinking to die before having to obey God commanding him to preach to Nineveh. God preserved Jonah using a great fish that spat Jonah upon the very shores of Nineveh. Jonah did not get out of his duty God gave him. And when Jonah had preached to them and saw God had repented of His warning to destroy Nineveh, Jonah was angry because he knew they would be saved. (the reason why Jonah wanted them destroyed is another topic). The point being, that with those who God 'sent', He will directly influence their own wills and keep them in line of their service to Him. In other words, it is impossible for those chosen sent ones to stray from God.
This is why our Lord Jesus would say the following about His chosen elect regarding the coming pseudo-Christ...
Matt 24:23-24
23 Then if any man shall say unto you, Lo, here is Christ, or there; believe it not.
24 For there shall arise false Christs, and false prophets, and shall shew great signs and wonders; insomuch that, if it were possible, they shall deceive the very elect.
(KJV)
The meaning about His very elect there is that it is impossible for those to be deceived. Again why? Because Christ already owns those. He can influence them directly so as to not be deceived, no matter what. What about those of us who not chosen sent ones, i.e., not "very elect" like those whom it is impossible to be deceived? We can be, IF... we allow ourselves to be deceived. It's because our Heavenly Father and His Son still allow us to use our free will choice to stray from Him. This is why His Apostles continually admonished the Churches to stay focused on Christ and be on guard, watching, and stay in the Faith they handed down to us by The Gospel. That is why Christ's Apostles would warn us about the end times being very perilous times for the brethren, because if we let our guard down, the enemies of Christ will deceive us, while His very elect won't be deceived by any man or thing.