Though this teaching may be popular, it is far from the truth of Scripture, and nothing even remotely hints at it; worst, it‘s a “damnable heresy” (2 Pet 2:1), which is a heresy that damns souls to hell. And this is nothing to say of how it greatly dishonours God, glorifies doubt and completely changes salvation and the gospel. People who embrace this heresy and reject the eternal security of salvation (which is salvation), don’t understand the true gospel of Jesus Christ according to Scripture. There are hundreds of passages of Scripture, OT and NT, that clarify how eternally secure salvation really is, and then none that speak against it.
If salvation isn’t permanent, it isn’t salvation, for that is the only way the Bible describes it. If you don’t have eternal security of salvation, you have never received the true gospel. The gospel has been distorted for you. Its a perverted “gospel of Christ” founded upon a lie (Gal 1:6-9), and you have placed your trust in something that is not true. You have been deceived. You might think you are a Christian but you have heard and believed a lie. If you believe one can fall away and lose his salvation, you have fallen away from the truth (apostatized) and have never been saved. And you aren’t in a class of your own; the Bible is full of such examples, of unsaved religious hypocrites.
The “salvation which is in Christ Jesus” comes with “eternal life” (Jn 3:15-16; 5:24; 10:27-29) and “eternal glory” (2 Tim 2:10). Salvation is being “born of God” by receiving the Lord Jesus Christ (Jn 1:12-13), and receiving Him is receiving “eternal life” (I Jn 1:1-3; Jn 17:2-3). Speaking of Christ, John said, “that eternal life, which was with the Father, and was manifested unto us” (1 Jn 1:2). Jesus is “that eternal life,” (see also Jn 5:39), the “life” (Jn. 14:6; I Jn. 1:1; Pr. 8:35), which “life” He gives at salvation (Jn 5:40; Jn 10:10; 17:2-3), “For whoso findeth me” Jesus said, “findeth life” (Pr 8:35) and He then indwells those born again (Gal 2:20).
Salvation, Jesus Christ, life and eternal life are all inseparable. They dovetail. If you don’t have one, you don’t have any. If you don't have eternal security, then you don’t have salvation, life or Christ. It’s that simple. Nothing complicated about it. False teachers complicate things, because they reject and replace the true gospel with their own version, a version that magnifies their own self-righteousness, but “they being ignorant of God's righteousness, and going about to establish their own righteousness, have not submitted themselves unto the righteousness of God. For Christ is the end of the law for righteousness to every one that believeth.”(Rom 10:3-4)
The passages that are sometimes used in attempt to support “losing salvation” doctrine have to be twisted completely out of context, privately interpreted, falsely divided, misused and abused to achieve their desired end. But this is an “error of the wicked,” which are false teachers who are “unlearned and unstable,” who “wrest the scriptures, unto their own destruction.” (2 Pet 3:16-17). Concerning any “doctrine of Christ” (2 Jn. 1:9), which would include salvation and eternal security thereof, “If there come any unto you, and bring not this doctrine, receive him not into your house, neither bid him God speed: For he that biddeth him God speed is partaker of his evil deeds.” (2 Jn 1:10-11).
The Bible actually specifically teaches that if you reject eternal security of salvation which God gives at conversion, and embrace the heresy of losing salvation, you are not saved at all nor have you ever been, and this is for three very important reasons detailed in 1 Jn 5:10-13 which reads:
“He that believeth on the Son of God hath the witness in himself: he that believeth not God hath made him a liar; because he believeth not the record that God gave of his Son. And this is the record, that God hath given to us eternal life, and this life is in his Son. He that hath the Son hath life; and he that hath not the Son of God hath not life. These things have I written unto you that believe on the name of the Son of God; that ye may know that ye have eternal life, and that ye may believe on the name of the Son of God.”
Three very important reasons why you are unsaved, i.e., never been saved:
You reject the record that God gave of His Son, which is eternal life;
You make God a liar; and
You do not have the indwelling witness, which is God the Spirit.
Notice that all four things mentioned above: salvation, Jesus Christ the Son of God, life and eternal life are presented here as being received at the very moment of true repentant faith. They all tie together with God’s record of eternal life through His precious Son the Lord Jesus Christ.
The losing salvation heresy however contradicts and lies against “the record that God gave of His Son” which “is the record, that God hath given to us eternal life, and this life is in his Son” (vv 10-11). By rejecting this truth and making God a liar (how terribly fearful is that!), these people reveal themselves to be without the indwelling witness, for “He that believeth on the Son of God hath the witness in himself” for “believeth …the record that God gave of his Son” and we know that witness is actually the Holy Spirit of God, as seen further in the context (1 Jn 5:6-9), Whom is received at salvation (Ac 2:38; 10:45; 11:17; Eph 1:13-14; 1 Cor 6:19-20), and is the Spirit of Truth, not error and He does not teach lies to those He indwells, but truth alone and that to all He indwells (1 Jn 2:20-21, 27), so him who has not “the witness in himself” is obviously not saved, which is why he has no qualms about lying about God, for he is blind, deaf, uncircumcised of heart and dead in his sins. But “Knowledge is easy to him that understandeth” (Pr 14:6), and God’s words “are all plain to him that understandeth, and right to them that find knowledge.” (Pr 8:9). Believing God’s record of eternal life is plain for him with understanding, or in other words, him that is converted, for he has understanding (Pr 14:33; 17:24), while the false pretender does not.
These passages in 1 Jn 5 make it very clear that someone who believes eternal life can be lost, actually reject the record of God of eternal life through His Son, make God out to be a liar, and do not have the indwelling Spirit of God. Yes, they are unsaved, regardless of their sincerity, smiles, friendliness, or how much of scripture they supposedly get right or how they dress or how dedicated they are to church. The truth is, most of what such people teach and believe is distorted, confusing and contradictory. They are unable to rightly divide the word of truth, for they are without the “Spirit of truth,” who teaches the absolute truth of God’s Word to those He indwells (Jn 14:17; 15:26; 16:13).
God the Spirit is not glorified in this damnable heresy.
"False teachers" are the purveyors of "damnable heresies" (2 Pet 2:1) and they typically have a large following (2 Pet 2:2).
The heresy of losing salvation is just another form of works salvation. If you believe this "damnable heresy," (2 Pet 2:1) your justification is not that of grace, but rather grace plus works, which is not grace at all (Rom 11:6; Gal 5:1-4). You reject the true “grace of God that bringeth salvation” (Ti 2:11) and have believed in “another gospel” (2 Cor 11:4). You also reject justification, striving to stand before God in your own “righteousness” which the Bible calls “filthy rags” (Is 64:6), while true believers are justified, not by anything they’ve done or ever will do, but by Christ’s perfect righteousness (Rom 5:19) through repentant faith (Rom 5:1) at one moment in time (2 Cor 6:2).
For further reading on this subject, please go to Biblical Reasoning Why Salvation Can Never Be Lost.