This lesson examines the fifth point of Calvinism. This point is called "Perseverance of the Saints" to make the P in TULIP. This name falls short of really describing the doctrine. The doctrine is also referred by the following names, the last two being the most descriptive of what the doctrine really says...
"Infallible Grace"
"Eternal Security of the Believer"
"Impossibility of Apostasy"
"Once Saved Always Saved"
Whatever we call it, the doctrine involves a very simple question: Can a saved person cease to be saved and become lost again? The doctrine of the perseverance of the saints answers that question emphatically: No! The saints...
"can neither totally nor finally fall away from the state of grace but shall certainly persevere therein to the end and be eternally saved".
But is that answer correct?
The Broad Basis of the Idea
The doctrine of Impossibility of Apostacy is the logical outcome of the other four points of Calvinism, and of the peculiar view of God's sovereign will which underlies all the points. If you hold to those points, and to that view, then you have to hold the "Once Saved Always Saved" doctrine as well, if you are to be consistent.
Suppose, for argument's sake, that you believe people are totally unable to contribute anything toward their own salvation, unable even so much as to desire or seek that salvation. Those who are saved, are saved by God's decision and God's power alone. The Father chose them, the Son redeemed them, and the Holy Spirit called them. The people themselves had nothing whatever to do with their salvation. It was all of God, wholly and solely by his will, his grace, his power. If you believe that, then it is inconceivable to you that any saved person could be lost, because God is invincible. If God has done it all by himself, then certainly nobody can ever cause it to be undone.
That is the philosophy behind "Once Saved Always Saved" or the "Perseverance of the Saints". Now let us briefly notice some specific arguments made by those who hold the doctrine.
The Specific Arguments of the Doctrine
1. That Jesus prays for the saint's salvation (Jhn 17:24). Jesus "makes intercession for the saints according to the will of God" (Heb 7:25 Rom 8:27). If any saved person is lost in the end, then God has denied Jesus the answer to his prayers.
Reply to argument 1... Christ always prayed in submission to God's eternal purpose. For example, before he went to the cross, Jesus unashamedly expressed his desire to escape death upon the cross, while at the same time expressing his understanding of why his prayer could not be granted (Mtt 26:39).
No prayer of Christ is granted simply because it is his prayer. Other factors must be considered. It is wonderful to think that Jesus died on the cross for me, and that Jesus prays for me. But I will be in glory not simply because Jesus died for me and prays for me. Other factors must be considered. My own personal commitment, my own daily cross bearing, is one of those factors (Mtt 16:24).
2. That the saved are sealed by the Holy Spirit (Eph 1:13). How can anybody break the seal of God?
Reply to argument 2... The seal is "the guarantee of our inheritance" (Eph 1:14). Three things are assured.
Firstly, the God of the elect knows them as his own (2Tm 2:19). Secondly, no enemy of the elect can snatch them from Christ's hand (Jhn 10:28). Thirdly, the elect themselves can remain faithful to God (Rev 2:10).
This third guarantee, that the saved can certainly be faithful unto death, is the scriptural version of the perseverance of the saints. It is one thing to guarantee people that they can be faithful till the end, and nobody can force them to lose their salvation. It is quite another thing to say they are unable to fall. That gives them a false sense of security, not true and scriptural security.
3. That the saved already have eternal life (1Jn 5:11-12) If the saved have been given life everlasting, then that life cannot come to an end, because if it did, it would prove not to have been everlasting after all.
Reply to argument 3... When John said that we have eternal life, he did not mean that we have it outright in the final sense. He meant, as he previously explained, that we have it as a promise, and that promise is conditional (1Jn 2:24-25). If you would like more detail on this point, read Do We Already Have Eternal Life?.
4. That salvation is the free gift of God (Eph 2:8). Would God be so fickle as to give a gift, and then later demand that it be returned to him?
Reply to argument 4... God never changes his mind and retracts his promise, nor does God ever demand his gift back. By grace, he has given us the promise and hope of eternal life on the condition that we continue in the faith (Col 1:23). Eternal life is a free gift in the sense that it is unmerited, not in the sense that it is unconditional.
If I gave you a holiday as a free gift, it would be conditional upon you actually making the journey to the retreat. If you decided not to go, or got half way and decided to quit, that would not mean I had changed my mind or demanded my gift back. It would be all your doing.
The Possibility of Apostasy
In this section of the lesson, we are going to see from the scripture that it is possible to fall from grace. We will lay some groundwork, then prove the point. Please follow the steps carefully.
The Saved and Sanctified People in Hebrews 10
In Hebrews 10 the writer addresses certain remarks to a definite group of "brethren" whom he knew very well. In verses 32-34 he recalls how he and they had endured persecution together. Throughout the chapter he says several things which he believed to be true of himself and them.
Firstly he says, "By God's will we have been sanctified through the offering of the body of Jesus Christ" (verse 10). The writer considered that he and the brethren he was writing to were sanctified, isn't that so?
Secondly the saints were "perfected forever" according to verse 14. If the people were sanctified by Christ's offering, then they were "perfected forever". That's quite clear there in verse 14, isn't it?
Thirdly through Christ their High Priest they could have the "full assurance of faith" as stated in verses 19-22. Satisfy yourself that the writer and the people he was writing to were sanctified by the body and blood of Christ, were perfected forever, and fully assured of their salvation. Isn't that true?
Those Same People Could Fall Away
Now looking through the rest of the chapter, ask yourself whether it was possible for them to lose what they had gained.
Firstly note the exhortation in verse 23, "Let us hold fast to the hope we profess." Doesn't that imply that it was possible for them to let go of their hope?
Secondly note the warning in verses 26-27, "For if we sin willfully..." Satisfy yourself that this is the same "we" to whom the writer refers in the above passages --that is to say we who are sanctified, perfected forever, fully assured.
Thirdly note the consequences in verses 26-27, of letting go of the hope and of sinning willfully. "There remains no more a sacrifice for sins, but a certain expectation of judgment, and fiery indignation which shall devour the adversaries". Upon whom do these consequences come? The "we" in the phrase "If we sin willfully..." The same "we" and "us" that were said to be sanctified, perfected forever, and fully assured.
It is clear from this examination of Hebrews 10 that the very ones who were sanctified, perfected forever, fully assured, and could hold fast to their hope, were the same ones who could sin willfully, be left without a sacrifice for their sins, become God's adversaries, and be subject to damnation? In short they could either persevere, or they could fall away.
In verse 39 there is the happy statement, "But we are not of those who draw back to perdition, but of those who believe to the saving of the soul".
Did he say it was impossible for them to draw back to perdition and that the only thing possible for them was believing to the saving of the soul? No. But he did express their firm resolve. It was possible to draw back to perdition, and some folk do (1Pe 2:20-22). However, it was also perfectly possible to persevere in believing to the saving of the soul, and that is what the writer and his brethren had resolved to do.
May you, dear friend, do likewise, and may God give you every encouragement.
Firstly, the God of the elect knows them as his own 
It is clear from this examination of Hebrews 10 that the very ones who were sanctified, perfected forever, fully assured, and could hold fast to their hope, were the same ones who could sin willfully, be left without a sacrifice for their sins, become God's adversaries, and be subject to damnation? In short they could either persevere, or they could fall away.