The question of the "eternal security of the believer" has been the cause of much controversy in the church for centuries—and still creates confusion and distress for many Christians. It is too much to expect to dispel this problem completely for everyone in a brief tract, but perhaps we can at least help in that direction.
Those who believe in "falling away" accuse those who believe in "eternal security" of promoting "cheap grace." While it may be a convenient expression, the latter phrase is of course unbiblical. To call it "cheap" is really a denial of grace, since it implies that too small a price has been paid. Grace, however, must be absolutely free and without any price at all on man's part; while on God's part the price He paid was infinite. Thus for man to think that his works can play any part in either earning or keeping his salvation is what cheapens grace, devaluing this infinite gift to the level of human effort.
To speak of "falling from grace" involves the same error. Since our works had nothing to do with meriting grace in the first place, there is nothing we could do that would cause us no longer to merit it and thus "fall" from it. Works determine reward or punishment—not one's salvation, which comes by God's grace. The crux of the problem is a confusion about grace and works.
In the Greek, Christ's cry from the cross, "It is finished!" is an accounting term, meaning that the debt had been paid in full. Justice had been satisfied by full payment of its penalty, and thus God could "be just, and the justifier of him which believeth in Jesus" (Rom 3:26). On that basis, God offers pardon and eternal life as a free gift. He could not force it upon anyone or it would not be a gift. Nor would it be just to pardon a person who rejects the righteous basis for pardon and offers a hopelessly inadequate payment instead—or offers his works even as "partial payment."
Salvation is the full pardon by grace from the penalty of all sin, past, present or future; eternal life is the bonus thrown in. Denying this cardinal truth, all cultists, such as Jehovah's Witnesses, for example, reject salvation by grace and insist that it must be earned by one's good works. They accuse evangelicals of teaching that all we need to do is to say we believe in Christ and then we can live as we please, in the grossest of sins, yet be sure of heaven. Evangelicals don't teach that at all, yet a similar complaint is made by those who believe in "falling away." They say that "once saved, always saved" encourages one to live in sin because if we know we cannot be lost we have no incentive for living a holy life. On the contrary, love for the One who saved us is the greatest and only acceptable motive for living a holy life; and surely the greater the salvation one has received, the more love and gratitude there will be. So to know one is secure for eternity gives a higher motive for living a good life than the fear of losing one's salvation if one sins!
While those who believe in "falling from grace" are clear that good works cannot earn salvation, they teach that salvation is kept by good works. Thus one gets saved by grace, but thereafter salvation can be lost by works. To teach that good works keep salvation is almost the same error as to say that good works earn salvation. It denies grace to say that once I have been saved by grace I must thereafter keep myself saved by works.
Such teaching, says Hebrews 6:4-9, rather than glorifying Christ, once again holds Him up to shame and ridicule before the world once again for two reasons: if we could lose our salvation, then (1) Christ would have to be crucified again to save us again; and (2) He would be ridiculed for dying to purchase a salvation but not making adequate provision to preserve it—for giving a priceless gift to those who would inevitably lose it. If Christ's dying in our place for our sins and rising again was not sufficient to keep us saved, then He has foolishly wasted His time. If we could not live a good enough life to earn salvation, it is certain we cannot live a good enough life to keep it! To make the salvation he procured ultimately dependent upon our works would be the utmost folly.
"Falling away" doctrine makes us worse off after we are saved than before. At least before conversion we can get saved. But after we are saved and have lost our salvation (if we could), we can't get saved again, but are lost forever. Hebrews 6:4-6 declares, "If [not when] they shall fall away...it is impossible (v 4)...to renew them again unto repentance." That "falling away" is hypothetical is clear (v 9): "But, beloved, we are persuaded better things of you, and things that accompany salvation, though we thus speak." So "falling away" does not "accompany salvation." The writer is showing us that if we could lose our salvation, we could never get it back without Christ dying again upon the cross. Such thinking is folly! He would have to die an infinite number of times (i.e., every time every once-saved person sinned, was lost, and wanted to be "saved again"). Thus, those who eject "once saved, always saved," can only replace it with, "once lost, always lost!"
John assures us, "These things have I written unto you that believe on the name of the Son of God; that ye may know [present knowledge] that ye have [present possession] eternal life..." (1 Jn 5:13). To call it eternal life would be a mockery if the person who had it could lose it and suffer eternal death. On the contrary, eternal life is linked with the promise that one cannot perish—a clear assurance of "eternal security" or "once saved, always saved." John 3:16 promises those who believe in Jesus Christ that they "should not perish, but have everlasting life." John 5:24 again says, "hath everlasting life, and shall not come into condemnation...." One could not ask for clearer or greater assurance than the words of Jesus: "I give unto them [my sheep] eternal life; and they shall never perish" (Jn 10:28). If, having received eternal life, we could lose it and perish, it would make Christ a liar.
If sin causes the loss of salvation, what kind or amount of sin does it take? There is no verse in the Bible that tells us. We are told that if we confess our sins He is faithful and just to forgive us and to cleanse us from all unrighteousness—so apparently any sin can be forgiven. Even those who teach falling away rarely if ever say they got "saved again." Rather, they confessed their sin and were forgiven. Hebrews 12:3-11 tells us that every Christian sins, and that instead of causing a loss of salvation, sin brings God's chastening upon us as His children. If when we sinned we ceased to be God's children, He would have no one to chastise—yet he "scourgeth every son whom he receiveth." Indeed, chastening is a sign that we are God's children, not that we have lost our salvation: "if ye be without chastisement, whereof all are partakers, then are ye bastards, and not sons."
Some teach that one must be baptized to be saved; others that one must "speak in tongues." Both are forms of salvation by works. Some people lack assurance of salvation because they haven't "spoken in tongues," others are confident they are saved because they think they have. Both are like those who say, "Lord, Lord, have we not...in thy name done many wonderful works?" (Mt 7:21-23). They are relying on their works to prove they are saved, instead of upon God's grace. Nor does Jesus say, "You were once saved but lost your salvation." He says, "I never knew you."
Here is an important distinction. Those who believe in "falling away" would say of a professing Christian who has denied the faith and is living in unrepentant sin that he has "fallen from grace" and has "lost his salvation." In contrast, those who believe in "eternal security," while no more tolerant of such conduct, would say of the same person that probably Christ "never knew him"—he was never a Christian. We must give the comfort and assurance of Scripture to those who are saved; but at the same time we must not give false and unbiblical comfort to those who merely say they are saved but deny with their lives what they profess with their lips.
Are we not then saved by our works? Indeed not! In 1 Corinthians 3:12-15 every Christian's works are tried by fire at the "judgment seat of Christ" before which "we must all appear" (2 Cor 5:10). Good works bring rewards; a lack of them does not cause loss of salvation. The person who hasn't even one good work (all of his works are burned up) is still "saved; yet so as by fire" (1 Cor 3:15). We would not think such a person was saved at all. Yet one who has truly received the Lord Jesus Christ as his Savior, but who has no good works as evidence and may seem outwardly not to be a Christian, is "saved as by fire" and shall never perish in spite of his lack of works.
Do we then, on the basis of "once saved, always saved," encourage Christians to "sin that grace may abound?" With Paul we say, "God forbid!" We offer no comfort or assurance to those living in sin. We don't say, you're okay because you once made a "decision for Christ." Instead, we warn, "If you are not willing right now to live fully for Christ as Lord of your life, how can you say that you were really sincere when you supposedly committed yourself to Him at some time in the past?" And to all we declare with Paul, "Examine yourselves, whether ye be in the faith; prove your own selves" (2 Cor 13:5).
Our confidence for eternity rests in His unchanging love and grace and the sufficiency of God's provision in Christ—not in our worth or performance. Only when this is clear do we have real peace with God. Only then can we truly love Him and live for Him out of gratitude for the eternal life He has given to us as a free gift of His grace—a gift He will not take back and which He makes certain can never be lost!