It is very sad how many believers are going around thinking that they can somehow save themselves. This is essentially what one must believe if one thinks that salvation can be lost. But Scripture is absolutely clear on this point: No one can even begin to desire to be saved if God has not imparted that desire to them. Every child of God was once "dead in trespasses and sins" (Eph. 2:1), alienated from God and enemies in their minds toward Him by wicked works (Col. 1:21), and of a fleshly, carnal mind that did not possess the capacity to obey God (Ro. 8:7). In such a condition, there is no way anybody could ever save themselves or even seriously consider doing so of their own accord. This is why Jesus said,
John 6:44-45
44 No one can come to Me unless the Father who sent Me draws him; and I will raise him up at the last day.
45 It is written in the prophets, 'And they shall all be taught by God.' Therefore everyone who has heard and learned from the Father comes to Me.
Our utter inability to be who God commands us to be in and of ourselves is only part of the issue, however. God has so ordained things such that He will give us not the slightest reason to boast in the matter of our salvation. The salvation of God is a monergistic work of God in us; He does it all.
Ephesians 2:8-9
8 For by grace you have been saved through faith, and that not of yourselves; it is the gift of God,
9 not of works, lest anyone should boast.
Titus 3:4-7
4 But when the kindness and the love of God our Savior toward man appeared,
5 not by works of righteousness which we have done, but according to His mercy He saved us, through the washing of regeneration and renewing of the Holy Spirit,
6 whom He poured out on us abundantly through Jesus Christ our Savior,
7 that having been justified by His grace we should become heirs according to the hope of eternal life.
Clearly, then, salvation cannot in any way be of us. Our role in our salvation is simply to receive it by faith. But if our salvation is not our doing, how can it be our responsibility to retain it? If we are so incapable of saving ourselves, how can we possibly be expected to keep ourselves saved? Such an expectation is akin to saving a drowning quadraplegic by putting a lifejacket on him and then demanding that he swim himself to shore!
Thankfully, this is not what Scripture teaches concerning the maintenance of our salvation. God is very plain in His Word that He has assumed the responsibility for preserving our adoption into His family.
Philippians 1:6
6 being confident of this very thing, that He who has begun a good work in you will complete it until the day of Jesus Christ;
Philippians 2:13
13 for it is God who works in you both to will and to do for His good pleasure.
Hebrews 12:2
2 looking unto Jesus, the author and finisher of our faith...
Jude 1:24
24 Now to Him who is able to keep you from stumbling, And to present you faultless Before the presence of His glory with exceeding joy,
And so on.
What, then, of those infamous verses which seem to indicate that one can lose one's salvation? Well, they are not meant to be read in isolation, but in their immediate context and in the larger context of all of Scripture. And when this is how they are read, it is not so clear that they are teaching a saved-and-lost doctrine.
John 15:2
2 Every branch in Me that does not bear fruit He takes away; and every branch that bears fruit He prunes, that it may bear more fruit.
No mention of hell here. The threat of Hell must be read into what Jesus says in this verse. At most, "takes away" could be understood to mean that God ends a believer's life when it is clear they are not going to bear spiritual fruit.
John 15:6
6 If anyone does not abide in Me, he is cast out as a branch and is withered; and they gather them and throw them into the fire, and they are burned.
This seems like a much more explicit declaration of a saved-and-lost doctrine but if we let Scripture explain itself, it becomes quickly apparent that loss of salvation and hell are not in view in Jesus' comments:
Ezekiel 15:1-5
1 Then the word of the Lord came to me, saying:
2 "Son of man, how is the wood of the vine better than any other wood, the vine branch which is among the trees of the forest?
3 Is wood taken from it to make any object? Or can men make a peg from it to hang any vessel on?
4 Instead, it is thrown into the fire for fuel; the fire devours both ends of it, and its middle is burned. Is it useful for any work?
5 Indeed, when it was whole, no object could be made from it. How much less will it be useful for any work when the fire has devoured it, and it is burned?
The prophet Ezekiel explains here that the wood of the vine is not particularly good for fashioning into useful items. A vine is chiefly valued for the fruit it produces. If, then, a vine does not bear fruit, it has little other use and is therefore typically used for firewood. Ezekiel's emphasis here is on the vine's usefulness, which is also the emphasis in Jesus' words in John 15. In fact, it seems very likely that Jesus' comments were a reference to Ezekiel's. But Ezekiel was in no way espousing or promoting a saved-and-lost doctrine - and neither is Jesus. What Jesus is commenting on in John 15:6 is the utter uselessness of a believer who does not bear spiritual fruit, not a saved-and-lost doctrine. The branches being "cast into the fire" is a picture of how totally useless fruitless branches are, not of losing one's salvation.
So, what about Hebrews 10:26 and 27?
Hebrews 10:26-27
26 For if we sin willfully after we have received the knowledge of the truth, there no longer remains a sacrifice for sins,
27 but a certain fearful expectation of judgment, and fiery indignation which will devour the adversaries.
The reality is that every believer at one time or another - and often repeatedly - sins willfully. Paul the apostle explains why:
Galatians 5:17
17 For the flesh lusts against the Spirit, and the Spirit against the flesh; and these are contrary to one another, so that you do not do the things that you wish.
So it is that the apostle John writes,
1 John 1:8
8 If we say that we have no sin, we deceive ourselves, and the truth is not in us.
In light of these verses, how are we to understand Hebrews 10:26, 27? Clearly, the writer of Hebrews cannot be telling us that every time we sin we lose our salvation! If that were so, all of what Paul writes to us of justification by faith is meaningless! Obviously, this is not an option. So, how, then, to understand Hebrews 10:26, 27? It seems to me that the phrase "receiving a knowledge of the truth" cannot refer to salvation. Many people "receive a knowledge of the truth" when they hear the Gospel, but they turn from its precious truths - and from the sole means of reconciliation with God they hold out - and, as the writer of Hebrews explains, in so doing place themselves under God's wrath. This interpretation accords easily and well with the immediate context, the rest of Scripture, and avoids any eisegesis.
Finally, what about this passage?:
Hebrews 6:4-6
4 For it is impossible for those who were once enlightened, and have tasted the heavenly gift, and have become partakers of the Holy Spirit,
5 and have tasted the good word of God and the powers of the age to come,
6 if they fall away, to renew them again to repentance, since they crucify again for themselves the Son of God, and put Him to an open shame.
Again, this looks like a clear saved-and-lost passage. I would contend, however, that this is so only if such a reading is imported into the passage. Of itself, the passage does not teach one can be saved and lost. At most, it explains that there is only one way by which we can be reconciled to God: through the atoning sacrifice of Jesus Christ. If a believer - for that is clearly who the passage is describing - willfully falls away from walking with God, rejecting the only means by which they can be restored to fellowship with God, they confirm themselves in a permanently prodigal condition. But just as the Prodigal Son never ceased to be his father's son no matter how far he strayed, no born-again believer ceases to be the adopted child of their Heavenly Father no matter how far they may stray from Him. A potent example of this is presented to us in 1Corinthians 5:
1 Corinthians 5:1-5
1 It is actually reported that there is sexual immorality among you, and such sexual immorality as is not even named among the Gentiles--that a man has his father's wife!
2 And you are puffed up, and have not rather mourned, that he who has done this deed might be taken away from among you.
3 For I indeed, as absent in body but present in spirit, have already judged (as though I were present) him who has so done this deed.
4 In the name of our Lord Jesus Christ, when you are gathered together, along with my spirit, with the power of our Lord Jesus Christ,
5 deliver such a one to Satan for the destruction of the flesh, that his spirit may be saved in the day of the Lord Jesus.
Paul does not declare the sinning brother anathema. He does not call him an unbeliever. No, Paul commanded the Corinthian believers to give up their incestuous Christian brother to Satan for "the destruction of his flesh, that his spirit may be saved." Paul enacts a corrective course with this sinning believer, not a disowning one. And, indeed, in Paul's second letter to the Corinthians he urges them to take once again into their fellowship the now sorrowful and repentant (but never unsaved) brother. (2Cor. 2:7)
For these and many other reasons I have not broached here, I cannot accept a saved-and-lost doctrine as biblical.
Selah.