I do not believe in "eternal security"...
at least in the way many Christians use that term today. I most certainly do believe that God eternally keeps those who are his. This is a powerful biblical truth and an anchor of the soul. However, the way many Christians think of eternal security amounts to the rotten remains of a once vibrant biblical doctrine called the perseverance of the saints. "Eternal security" is reduced to sloganeering - "once saved, always saved" - with no ability to handle the warning texts and teachings of Scripture. "Eternal security" is a form of sacramentalism - "pray this prayer and then don't ever doubt your salvation." "Eternal security" gives place to carnal indifference in the pilgrimage to glory.
No, the biblical teaching on this matter is much more robust, much more challenging, much more humbling, and much more satisfying than that. Read the fifth head of doctrine below carefully, and you will understand it well.
FIFTH HEAD OF DOCTRINE
Of the Perseverance of the Saints
Article 1. Whom God calls, according to his purpose, to the communion of his Son, our Lord Jesus Christ, and regenerates by the Holy Spirit, he delivers also from the dominion and slavery of sin in this life; though not altogether from the body of sin, and from the infirmities of the flesh, so long as they continue in this world.
Article 2. Hence spring daily sins of infirmity, and hence spots adhere to the best works of the saints; which furnish them with constant matter for humiliation before God, and flying for refuge to Christ crucified; for mortifying the flesh more and more by the spirit of prayer, and by holy exercises of piety; and for pressing forward to the goal of perfection, till being at length delivered from this body of death, they are brought to reign with the Lamb of God in heaven.
Article 3. By reason of these remains of indwelling sin, and the temptations of sin and of the world, those who are converted could not persevere in a state of grace, if left to their own strength. But God is faithful, who having conferred grace, mercifully confirms, and powerfully preserves them herein, even to the end.
Article 4. Although the weakness of the flesh cannot prevail against the power of God, who confirms and preserves true believers in a state of grace, yet converts are not always so influenced and actuated by the Spirit of God, as not in some particular instances sinfully to deviate from the guidance of divine grace, so as to be seduced by, and to comply with the lusts of the flesh; they must, therefore, be constant in watching and in prayer, that they be not led into temptation. When these are neglected, they are not only liable to be drawn into great and heinous sins, by Satan, the world and the flesh, but sometimes by the righteous permission of God actually fall into these evils. This, the lamentable fall of David, Peter, and other saints described in Holy Scripture, demonstrates.
Article 5. By such enormous sins, however, they very highly offend God, incur a deadly guilt, grieve the Holy Spirit, interrupt the exercise of faith, very grievously wound their consciences, and sometimes lose the sense of God's favor, for a time, until on their returning into the right way of serious repentance, the light of God's fatherly countenance again shines upon them.
Article 6. But God, who is rich in mercy, according to his unchangeable purpose of election, does not wholly withdraw the Holy Spirit from his own people, even in their melancholy falls; nor suffers them to proceed so far as to lose the grace of adoption, and forfeit the state of justification, or to commit sins unto death; nor does he permit them to be totally deserted, and to plunge themselves into everlasting destruction.
Article 7. For in the first place, in these falls he preserves them in the incorruptible seed of regeneration from perishing, or being totally lost; and again, by his Word and Spirit, certainly and effectually renews them to repentance, to a sincere and godly sorrow for their sins, that they may seek and obtain remission in the blood of the Mediator, may again experience the favor of a reconciled God, through faith adore his mercies, and henceforward more diligently work out their own salvation with fear and trembling.
Article 8. Thus, it is not in consequence of their own merits, or strength, but of God's free mercy, that they do not totally fall from faith and grace, nor continue and perish finally in their backslidings; which, with respect to themselves, is not only possible, but would undoubtedly happen; but with respect to God, it is utterly impossible, since his counsel cannot be changed, nor his promise fail, neither can the call according to his purpose be revoked, nor the merit, intercession and preservation of Christ be rendered ineffectual, nor the sealing of the Holy Spirit be frustrated or obliterated.
Article 9. Of this preservation of the elect to salvation, and of their perseverance in the faith, true believers for themselves may and ought to obtain assurance according to the measure of their faith, whereby they arrive at the certain persuasion, that they ever will continue true and living members of the church; and that they experience forgiveness of sins, and will at last inherit eternal life.
Article 10. This assurance, however, is not produced by any peculiar revelation contrary to, or independent of the Word of God; but springs from faith in God's promises, which he has most abundantly revealed in his Word for our comfort; from the testimony of the Holy Spirit, witnessing with our spirit, that we are children and heirs of God, Romans 8:16; and lastly, from a serious and holy desire to preserve a good conscience, and to perform good works. And if the elect of God were deprived of this solid comfort, that they shall finally obtain the victory, and of this infallible pledge or earnest of eternal glory, they would be of all men the most miserable.
Article 11. The Scripture moreover testifies, that believers in this life have to struggle with various carnal doubts, and that under grievous temptations they are not always sensible of this full assurance of faith and certainty of persevering. But God, who is the Father of all consolation, does not suffer them to be tempted above that they are able, but will with the temptation also make a way to escape, that they may be able to bear it, I Corinthians 10:13, and by the Holy Spirit again inspires them with the comfortable assurance of persevering.
Article 12. This certainty of perseverance, however, is so far from exciting in believers a spirit of pride, or of rendering them carnally secure, that on the contrary, it is the real source of humility, filial reverence, true piety, patience in every tribulation, fervent prayers, constancy in suffering, and in confessing the truth, and of solid rejoicing in God: so that the consideration of this benefit should serve as an incentive to the serious and constant practice of gratitude and good works, as appears from the testimonies of Scripture, and the examples of the saints.
Article 13. Neither does renewed confidence or persevering produce licentiousness, or a disregard to piety in those who are recovering from backsliding; but it renders them much more careful and solicitous to continue in the ways of the Lord, which he hath ordained, that they who walk therein may maintain an assurance of persevering, lest by abusing his fatherly kindness, God should turn away his gracious countenance from them, to behold which is to the godly dearer than life: the withdrawing thereof is more bitter than death, and they in consequence hereof should fall into more grievous torments of conscience.
Article 14. And as it hath pleased God, by the preaching of the gospel, to begin this work of grace in us, so he preserves, continues, and perfects it by the hearing and reading of his Word, by meditation thereon, and by the exhortations, threatenings, and promises thereof, as well as by the use of the sacraments.
Article 15. The carnal mind is unable to comprehend this doctrine of the perseverance of the saints, and the certainty thereof; which God hath most abundantly revealed in his Word, for the glory of his name, and the consolation of pious souls, and which he impresses upon the hearts of the faithful. Satan abhors it; the world ridicules it; the ignorant and hypocrite abuse, and heretics oppose it; but the spouse of Christ hath always most tenderly loved and constantly defended it, as an inestimable treasure; and God, against whom neither counsel nor strength can prevail, will dispose her to continue this conduct to the end. Now, to this one God, Father, Son, and Holy Spirit, be honor and glory, forever. AMEN.