1 Peter 1:9 - receiving the end of your faith -- the salvation of your souls. ~ Note: Beforehand, Peter was talking about enduring through trials we get tested by and having our genuine faith glorify God at the end. The word for trials also means adversity, affliction, trouble: sent by God and serving to test or prove one's character, faith, and holiness. This is like the chastening that God does to us found in 1 Cor. 11:32. We must persevere through whatever comes our way, all the way until the end; then we will be found good enough to be saved.
2 Peter 1:10 - Therefore, brethren, be even more diligent to make your call and election sure, for if you do these things you will never stumble. ~ Note: The word diligent also means endeavor, labour, to exert one's self. The word do also means to act rightly, do well, to carry out, to execute, to perform. Come on, just do it; so that you don't do this. The word stumble is fall in the KJV. I use the NKJV. It also means to err, make a mistake, to sin, to fall into misery, become wretched. So be firm in the faith, and make sure that you are born again and set free from the bondage of sin.
2 Peter 2:15,16 - They have forsaken the right way and gone astray, following the way of Balaam the son of Beor, who loved the wages of unrighteousness; but he was rebuked for his iniquity: a dumb donkey speaking with a man's voice restrained the madness of the prophet. ~ Note: God really meant business here. He has even made a dumb donkey speak with a man's voice to correct a person. To forsake the right way means to disregard and cease to care to do what is right in one's course of conduct. The word for gone astray also means to be led into error and sin. They were on the right way, but sin caused them to go astray.
2 Peter 2:20,21 - For if, after they have escaped the pollutions of the world through the knowledge of the Lord and Savior Jesus Christ, they are again entangled in them and overcome, the latter end is worse for them than the beginning. For it would have been better for them not to have known the way of righteousness, than having known it, to turn from the holy commandment delivered to them. ~ Note: The word knowledge means precise and correct knowledge, used in the NT of the knowledge of things ethical and divine. This is about real Christians who have been changed by the Lord Jesus Christ. They had the correct knowledge of Him. To be again entangled in the pollutions of the world means to be again involved in the foulness of the ungodly mass of mankind. The word overcome also means to be conquered by one, forced to yield to one. Here it means to be conquered by and forced to yield to sin. Then that makes the person a slave of sin again, as the previous verse, 2:19, implies. The word known in known the way of righteousness also means know well, to become thoroughly acquainted with. This is definitely about a former true Christian who was set free from sin, but then turned from that and became a slave of sin again. The latter end is one's last state. So these people will have a worse punishment in hell than if they never got saved to begin with.
BTW, some people try to say 2 Peter 2:20,21 is about the false teachers, but the context of Scripture proves that is not true. In 2 Peter 2:18 there is "For when they speak great swelling words of emptiness." THAT is the false teachers, but not the ones who the warning is for... "they allure through the lusts of the flesh, through lewdness, the ones who have actually escaped from them who live in error." Those are real Christians. They escaped already from the lost people who live in error. These saved people are what the warning of 2:20,21 is for. In 2 Peter 2:19 it has "While they promise them liberty." That's the false teachers promising liberty to real Christians. "they themselves are slaves of corruption; for by whom a person is overcome, by him also he brought into bondage." Yes, it proves the false teachers are lost, but it also is a warning to real Christians not to listen to the license to sin preachers, because they can wind up like them, overcome by and slaves of sin again. The word does not explain that false teachers try to allure real Christians with sin for nothing. Scripture is there to take heed to. So be careful of the alluring of the false teachers.
2 Peter 3:17,18 - You therefore, beloved, since you know this beforehand, beware lest you also fall from your own steadfastness, being led away with the error of the wicked; but grow in the grace and knowledge of our Lord and Savior Jesus Christ. To Him be the glory both now and forever. Amen. ~ Note: This clearly proves that "Once Saved, Always Saved" IS WRONG. To fall from also means to lose it, to perish, to fall powerless, be without effect of the divine promise of salvation. That happens when one is led away with the error of the wicked. The error of the wicked is the wrong opinion relative to morals or religion, a wrong mode of acting. The word wicked doesn't have to be someone very evil. It means one who breaks through the restraint of law and gratifies his lusts. So lustful sin is the issue. The grace of God doesn't allow you to gratify your lusts. If you are led away into that, this Scripture implies that you have lost your salvation.
1 John 2:24,25 - Therefore let that abide in you which you heard from the beginning. If what you heard from the beginning abides in you, you also will abide in the Son and in the Father. And this is the promise that He has promised us -- eternal life. ~ Note: God's love of giving us eternal life is conditional. The word if proves this. We must let the truth keep abiding in us. The KJV is a little different than the NKJV I use. It has: If that which ye have heard from the beginning shall remain in you, ye also shall continue in the Son and in the Father. ~ You see, getting saved is not a one time deal and it's all over with.
1 John 2:28 - And now, little children, abide in Him, that when He appears, we may have confidence and not be ashamed before Him at His coming. ~ Note: John is telling Christians to abide in Christ. What if they didn't abide? They wouldn't have confidence at the Lord's coming is what it implies. Why wouldn't they if they were "Once Saved, Always Saved?" You see, it doesn't make sense. "O.S.A.S." IS WRONG. The word confidence also means free and fearless confidence, cheerful courage, boldness, assurance. You see, if you do the condition of abiding in Christ, you can have assurance of your salvation. But this is not eternal security. There is the condition of continuing to remain abiding in Christ. In addition to remain and continue, abide also means not to depart, to last, endure, not to become another or different. I hope that you realize that this is our personal responsibility, and just because you abide in Christ today doesn't mean that you will definitely stay that way. Scripture proves that, because some have already turned aside after Satan (1 Tim. 5:15).
Revelation 2:5-7 - "Remember therefore from where you have fallen; repent and do the first works, or else I will come to you quickly and remove your lampstand from its place -- unless you repent... He who has an ear, let him hear what the Spirit says to the churches. To him who overcomes I will give to eat from the tree of life, which is in the midst of the Paradise of God." ~ Note: Surely, this is a threat from Christ to His church with the words or else. The word fallen also means to lose it, to perish, be without the effect of the divine promise of salvation. That means they lost their salvation. The word repent means to change one's mind for better, heartily to amend with abhorrence of one's past sins. They had to repent of the sin that made them fall. The word works also means an act, deed, thing done. They had to do the things they did when they were saved before they fell. The word overcome also means to conquer, of Christians that hold fast their faith even unto death against the power of their foes, and temptations and persecutions. They had to conquer the sin they had been tempted by that made them lose their salvation. This is the case for all backsliders.
I've seen someone write this is about the church ceasing to exist, but since the word fallen involves losing salvation, that would mean God was telling the entire church that they all lost salvation. Plus the words "He who has an ear, let him hear" makes this individually, as does "To him who overcomes." That proves this is not collectively of the entire church having the danger to be removed.
Revelation 2:10,11 - "Do not fear any of those things which you are about to suffer. Indeed, the devil is about to throw some of you into prison, that you may be tested... Be faithful until death, and I will give you the crown of life. He who has an ear, let him hear what the Spirit says to the churches. He who overcomes shall not be hurt by the second death." ~ Note: Christ tells us to be faithful until death then we will be given the crown of life; and if we overcome the testing we won't be hurt by the second death. If you have an ear to hear, you know that this means that if we don't remain faithful and don't overcome the testing, then we won't get the crown of life and we will be hurt by the second death. Clearly, we have to be faithful all the way until we die. We must hold onto our faith even unto death, or else we will be hurt by the second death, which is the lake of fire.
Revelation 3:1-5 - ..."I know your works, that you have a name that you are alive, but you are dead. Be watchful, and strengthen the things which remain, that are ready to die, for I have not found your works perfect before My God. Remember therefore how you have received and heard; hold fast and repent. Therefore if you will not watch, I will come upon you as a thief, and you will not know what hour I will come upon you. Nevertheless you have a few names in Sardis who have not defiled their garments; and they shall walk with Me in white, for they are worthy. He who overcomes shall be clothed in white garments, and I will not blot out his name from the Book of Life; but I will confess his name before My Father and before His angels." ~ Note: These people had the name of being a Christian thinking they had eternal life, but they had become spiritually dead. Some had the chance to live because He says they were only ready to die. The term "ready to die" is of eternal death. They are subject to eternal misery in hell. They were not living the life of how they first received the word. They had defiled their garments (by sin) and needed to overcome this to be worthy enough to eventually walk with Christ in white garments; or else He will blot out their name from the Book of Life. The word "defiled" is used in the NT of those who have not kept themselves pure from the defilement of sin, who have soiled themselves by fornication and adultery. You must overcome and conquer sin if you fell back into the bondage of it. Repent and turn back to God for help.
BTW, Revelation 13:8 proves that not everyone's name gets started in the Book of Life. Some people say everyone starts in the Book of Life to make it look like this Scripture above doesn't mean a loss of salvation from someone who was saved. But only saved people get their names written in the Book of Life. So this does mean saved people can get their names blotted out by God from the Book of Life. Then they would no longer be saved.
Revelation 3:16 - "So then, because you are lukewarm, and neither hot nor cold, I will vomit you out of My mouth." ~ Note: Christ wants to vomit these believers out of His mouth. Then they would not be in Christ anymore. In very vivid terms, the Lord rejects the half-hearted efforts of self-satisfied Christians. If someone has become wealthy and thinks they have need of nothing (Rev.3:17), they just might get vomitted out. The word "lukewarm" is of the condition of the soul wretchedly fluctuating between a torpor (a state of being inactive, sluggishness) and a fervour (great warmth of emotion, zeal) of love. If we really love God, we will obey and keep His word (John 14:21,23).
Revelation 22:19 - and if anyone takes away from the words of the book of this prophecy, God shall take away his part from the Book of Life, from the holy city, and from the things which are written in this book. ~ Note: Clearly this is saying that God will take away the eternal life that someone thinks they have, and also their part in heaven (the holy city) will be taken away, and also the final redemption in Revelation will be taken away. They all mean the same thing: "Once Saved, Always Saved" IS WRONG.