Some people do not believe a person can fall away once they are saved.
But the Bible says it can happen and warns against it.
2Pe 2:20 For if after they have escaped the pollutions of the world through the knowledge of the Lord and Saviour Jesus Christ, they are again entangled therein, and overcome, the latter end is worse with them than the beginning.
2Pe 2:21 For it had been better for them not to have known the way of righteousness, than, after they have known it, to turn from the holy commandment delivered unto them.
2Pe 2:22 But it is happened unto them according to the true proverb, The dog is turned to his own vomit again; and the sow that was washed to her wallowing in the mire.
These people were saved because they have escaped the pollutions of the world through the knowledge of the Lord and Saviour Jesus Christ.
And knew the way of righteousness.
They had an understanding to turn away from sins but they went back to the ways of the world.
Which it would have been better if they had not known the way of righteousness than to turn from it.
But this is correctable.
2Ti 2:19 Nevertheless the foundation of God standeth sure, having this seal, The Lord knoweth them that are his. And, Let every one that nameth the name of Christ depart from iniquity.
Gal 5:16 This I say then, Walk in the Spirit, and ye shall not fulfil the lust of the flesh.
Gal 5:22 But the fruit of the Spirit is love, joy, peace, longsuffering, gentleness, goodness, faith,
Gal 5:23 Meekness, temperance: against such there is no law.
Gal 5:24 And they that are Christ's have crucified the flesh with the affections and lusts.
When we repent of our sins and confess Christ we are to turn away from sins and allow the Spirit to lead us to abstain from sins.
Mat 7:21 Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven.
Mat 7:23 And then will I profess unto them, I never knew you: depart from me, ye that work iniquity.
2Ti 3:4 Traitors, heady, highminded, lovers of pleasures more than lovers of God;
2Ti 3:5 Having a form of godliness, but denying the power thereof: from such turn away.
2Ti 3:7 Ever learning, and never able to come to the knowledge of the truth.
Some people do not come to the truth and love sin more than God.
These people did not come to the understanding to abstain from sin led by the Spirit.
They would not let go of the flesh.
That is why Jesus said He never knew them.
And they were ever learning, and never able to come to the knowledge of the truth.
They were not saved and then went back to sin but they were not saved at all.
Because they did not have the understanding about repentance from the start.
Heb 6:4 For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost,
Heb 6:5 And have tasted the good word of God, and the powers of the world to come,
Heb 6:6 If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame.
These people were saved for they were enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost, and have tasted the good word of God, and the powers of the world to come.
But they fell away.
This falling away is not accepting Jesus but going back to sin because it says they cannot renew themselves again which they cannot be saved again.
Which means they lost salvation by believing an alternate reality whether atheist, another religion, or stopped believing Jesus is Lord and Savior.
If they do that they cannot come back to salvation for God will not permit it.
This is not correctable.
1Ti 4:1 Now the Spirit speaketh expressly, that in the latter times some shall depart from the faith, giving heed to seducing spirits, and doctrines of devils;
1Ti 4:2 Speaking lies in hypocrisy; having their conscience seared with a hot iron.
2Ti 4:2 Preach the word; be instant in season, out of season; reprove, rebuke, exhort with all longsuffering and doctrine.
2Ti 4:3 For the time will come when they will not endure sound doctrine; but after their own lusts shall they heap to themselves teachers, having itching ears;
2Ti 4:4 And they shall turn away their ears from the truth, and shall be turned unto fables.
The time will come that people will not want to hear the truth of the Bible but want to hear it according to the new age.
An example is this the new age movement that interprets the Bible and religions according to the occult and evolution, and people are going to evolve to be spiritual, and greater, and Jesus became an ascended master among others, and there is no personal God, but they honor the God of forces the power of the Cosmos, and the New Age Christ is the next world teacher.
Which some shall depart from the faith and follow a different reality of the Bible that there is no personal God and Jesus is not Lord and Savior.
These people cannot come back to salvation.
But if a person that is in the new age that has not acknowledged the truth but comes to the truth they can be saved.
But if they go back to the new age they cannot be saved again.
Rom 11:20 Well; because of unbelief they were broken off, and thou standest by faith. Be not highminded, but fear:
Rom 11:21 For if God spared not the natural branches, take heed lest he also spare not thee.
Rom 11:22 Behold therefore the goodness and severity of God: on them which fell, severity; but toward thee, goodness, if thou continue in his goodness: otherwise thou also shalt be cut off.
Heb 3:12 Take heed, brethren, lest there be in any of you an evil heart of unbelief, in departing from the living God.
Heb 3:13 But exhort one another daily, while it is called To day; lest any of you be hardened through the deceitfulness of sin.
Heb 10:38 Now the just shall live by faith: but if any man draw back, my soul shall have no pleasure in him.
Heb 10:39 But we are not of them who draw back unto perdition; but of them that believe to the saving of the soul.
And other places that warn the saints they can lose salvation if they do not do what is right.
1Co 13:13 And now abideth faith, hope, charity, these three; but the greatest of these is charity.
Gal 5:6 For in Jesus Christ neither circumcision availeth any thing, nor uncircumcision; but faith which worketh by love.
1Jn 3:18 My little children, let us not love in word, neither in tongue; but in deed and in truth.
1Co 13:5 thinketh no evil;
1Co 13:6 Rejoiceth not in iniquity, but rejoiceth in the truth.
Charity, love in action, is greater than faith.
And faith works by love.
So if there is no love then faith is void.
Which charity does not think an evil thought.
And does not rejoice in iniquity but rejoices in the truth to hate sin allowing the Spirit to lead them to abstain from sin.
People who hold on to sin that is not love then there is no salvation.
A person that is saved can lose salvation if they do not abide in the truth they once accepted.
Having an understanding of repentance for that is the way to be saved.
Some Churches say they cannot abstain from sin so the people do not get saved not having the understanding of repentance.
Which they have a form of godliness but do not allow the Spirit to lead them and love sin more than God.