Definitions

By the Gospel I mean the whole counsel of God, as taught authoritatively in Holy Scripture, which is in all its contents, from beginning to end, the revelation of Jesus Christ as Mediator between God and man.
By certainty or faith I mean the soul’s persuasion of, and commitment to, the truth of the Gospel: in a word, the saving commitment of the self to Jesus Christ, as he offers himself in his Gospel.
By security I mean the likelihood or probability of an individual person entering heaven. That is to say, a secure person is one who will be in heaven.
By assurance of salvation or assurance I mean, in contrast to certainty, the soul’s persuasion of its own security.

Propositions

Security is the possession of every person who is certain of the Gospel, of every person who has saving faith. All the children of God are secure from the moment of their salvation, indeed, from everlasting to everlasting, and after they come to faith (certainty) God will at no point and in no wise deal with them as lawbreakers, but as beloved children in whom he is well pleased.
It is the will of God for all who are in Christ to be assured, to come to have “the full assurance of hope” (Heb. 6:11), to boldly “enter with confidence the holy places by the blood of Jesus” and “draw near with true heart in full assurance of faith…without wavering” (Heb. 10:19ff.), to “confirm their calling and election” (2 Pet. 1:10), in order that “perfect love” may cast out all their fears (1 John 4:18), and they may sing triumphantly with the Psalmist, “the LORD is my light and my salvation, whom shall I fear?” (Ps. 27:1)
To this end, he has given them of his Spirit: “By this we know that we abide in him and he in us, because he has given us of his Spirit” (1 John 4:13); “And I will ask the Father, and he will give you another Helper, to be with you forever, even the Spirit of truth…I will not leave you as orphans; I will come to you…In that day you will know that I am in my Father, and you in me, and I in you” (John 14:15ff.); “The Spirit himself bears witness with our spirit that we are the children of God” (Rom. 8:16); “In him you also…were sealed with the promised Holy Spirit, who is the guarantee of our inheritance” (Eph. 1:13–14); “‘This is my covenant with them’, says the LORD, ‘My Spirit that is upon you’” (Is. 59:21).
This witness, the testimonium Spiritus Sancti salvationis (the testimony of the Holy Spirit concerning salvation), cannot be reduced to the certainty produced in saving faith, since it concerns the individual also.
Assurance, which is the effect of this ministry of the Holy Ghost in the lives of believers, though like faith the common possession of the children of God, varies in degree both between believers and within the lives of believers.
This is because assurance, although a work of the Holy Ghost, is not merely a mystical experience, but something produced in organic connection with the ordained means of grace as they are operative in the life of the believer: “But if we walk in the light, as he is in the light, we have fellowship with one another, and the blood of Jesus his Son cleanses us from all sin” (1 John 1:7)—assurance grows organically through walking in the light in communion with God’s people.
By abandoning these means of grace, therefore, the believer may greatly undermine his assurance. I do not say, nor do I claim to understand, how great an extent this may be, except that believers are “never utterly destitute of that seed of God, and life of faith, that love of Christ and the brethren, that sincerity of heart, and conscience of duty, out of which, by the operation of the Spirit, this assurance may, in due time, be revived; and by the which, in the meantime, they are supported from utter despair” (WCF 18.4). However, I do say that it is certain that assurance may be shaken. This is why it is dangerous to live in sin: while a believer does not shake his security, in shaking his assurance he may come to that awful place in which he does not know if he is secure. Then he is the man whom Peter describes as “so nearsighted that he is blind, having forgotten that he was cleansed from his former sins” (2 Pet. 1:9). He can no longer separate between himself and the apostate (who never knew the Lord) until he, as James instructs, cleanses his hands and purifies his heart, drawing near to God with wretchedness and mourning and weeping and gloom (Jam. 4:6ff). As Sinclair Ferguson puts it,

We may take it as axiomatic that high degrees of true assurance cannot be enjoyed by those who persist in low levels of obedience. There is only one answer when [carnal inconsistency] gains the ascendency. We need to be led afresh by the Spirit, to show that we are sons of God by mortifying the deeds of the flesh (Rom. 8:13-14). Assurance in this respect always accompanies single-mindedness. It is the double-minded man only who is unstable (lacks assurance) in all his ways (Jam. 1:8).
It is important that believers know this assurance varies, so that when it is shaken, they do not fall into utter despair. For if the assurance of the godly cannot be shaken it follows plainly that he whose assurance is shaken is outside of Christ. Thus the Scripture presents us with examples of the godly: “Has God forgotten to be gracious?” (Ps. 77:9); “I had said in my alarm, ‘I am cut off from your sight’” (Ps. 31:21); “For when I kept silent, my bones wasted away through my groaning all day long” (Ps. 32:3); “Remove your stroke from me; I am spent by the hostility of your hand” (Ps. 39:10); “For I do not understand my own actions. For I do not do what I want, but I do the very thing I hate.” (Rom. 7:14ff.)
It is also important that believers know this assurance depends, in a measure, upon the means of grace, in order that they may cultivate it jealously. Hence the Scriptural commands to “confirm your calling and election” (2 Pet. 1:10), to “show earnestness to have full assurance” (Heb. 6:11). And it is taught plainly and repeatedly that this is done by walking in the light: “By this we know that we have come to know him, if we keep his commandments…whoever keeps his word, in him truly the love of God is perfected. By this we may know that we are in him: whoever says he abides in him ought to walk in the same way in which he walked” (1 John 2:3–6); “So we have come to know and to believe the love that God has for us. God is love, and whoever abides in love abides in God, and God abides in him. By this is love perfected with us, so that we may have confidence for the day of judgment, because as he is so also are we in this world.” (1 John 4:16–17)
The Bible comforts the sinner who desires holiness, but condemns the one who hardens his heart in sin. God’s kindness leads to repentance (Rom. 2:4) and God cannot be mocked, whatever a man sows, that shall he also reap (Gal. 6:7). “God opposes the proud but gives grace to the humble” is in this sense a summary of the Biblical doctrine of assurance: the proud can have no security, and should regard themselves as hanging on the precipice over hell; yet the humble, no matter how grave their transgressions, be they so many as the stars in heaven and so black as the heavens without stars, may always return to “an advocate with the Father, Jesus Christ the righteous” (1 John 2:1).
Good works done out of gratitude for God’s love and good works done in order to multiply and confirm assurance are so far from being in contradiction to one another that they are one and the same reality viewed from different angles. Good works are the expression of sonhood, the imitation of our Father, and such expression therefore, without being mercenary, feeds the conviction that this sonhood is a reality. So that to grow this conviction we seek to abound in good works, and where these works are absent or latent this conviction must needs be weakened.
It is not mercenary to seek to be conformed to the image of Jesus Christ in order that we may be assured. The mercenary attitude enters only at that point where our actions are done in order to achieve a reward which those actions are not organically related to. Full assurance is a fruit yielded in season on the tree that is the righteous man, planted by streams of water. Strangely, some who resist this understanding of assurance claim it trivialises union with Christ. And yet it does the very opposite: it insists that as Christ’s vitality flows into the believer, he will grow in obedience, and thereby be assured of his union with Christ. “By this my Father is glorified, that you bear much fruit and so prove to be my disciples” (John 15:8)—for as long as we keep our eyes fixed on this organic relationship there will be no difficulty in working for God’s glory and working to confirm our calling and election. It is right to seek assurance as the implication of living lives consecrated to God. It is not as if we say to God, “Give us assurance and we will give you works”, but instead we cry out with David, “Great peace have those who love your law; nothing can make them stumble” (Ps. 119:165). Does the sunflower turn itself in order to bask in the sun’s glory or in order to flourish? Isn’t this a false dichotomy? Do we not love God’s glory knowing that there is no higher good for us? “A man’s chief end is to glorify God and to enjoy him forever”—must these two be rent asunder? C.S. Lewis makes this point very clear in his famous address The Weight of Glory. I make no apology for quoting him at length:

The New Testament has lots to say about self-denial, but not about self-denial as an end in itself. We are told to deny ourselves and to take up our crosses in order that we may follow Christ; and nearly every description of what we shall ultimately find if we do so contains an appeal to desire. If there lurks in most modern minds the notion that to desire our own good and earnestly to hope for the enjoyment of it is a bad thing, I submit that this notion has crept in from Kant and the Stoics and is no part of the Christian faith. Indeed, if we consider the unblushing promises of reward and the staggering nature of the rewards promised in the Gospels, it would seem that Our Lord finds our desires, not too strong, but too weak. We are half-hearted creatures, fooling about with drink and sex and ambition when infinite joy is offered us, like an ignorant child who wants to go on making mud pies in a slum because he cannot imagine what is meant by the offer of a holiday at the sea. We are far too easily pleased.

We must not be troubled by unbelievers when they say that this promise of reward makes the Christian life a mercenary affair. There are different kinds of reward. There is the reward which has no natural connexion with the things you do to earn it, and is quite foreign to the desires that ought to accompany those things. Money is not the natural reward of love; that is why we call a man mercenary if he marries a woman for the sake of her money. But marriage is the proper reward for a real lover, and he is not mercenary for desiring it. A general who fights well in order to get a peerage is mercenary; a general who fights for victory is not, victory being the proper reward of battle as marriage is the proper reward of love. The proper rewards are not simply tacked on to the activity for which they are given, but are the activity itself in consummation.
Believers should therefore have no qualms about encouraging one another to work for the reward of multiplied assurance. Provided that this is done without suggesting that salvation is by works, we are well within the bounds of Scripture. Listen to the Saviour, “Whoever has my commandments and keeps them, he it is who loves me. And he who loves me will be loved by my Father, and I will love him and manifest myself to him.” (John 14:21) Tell me, does he foster works-based salvation and the self-righteous attitude? Does anyone dare accuse him of undermining the principle of grace which he himself enacted into operation that very night? Does he teach that God loves us because we keep his law? The truth is that God assures us he loves us—and that we love him—by empowering us to keep his law. The New Covenant involves God writing his law on the hearts of his people: “I will put my law within them, and I will write it on their hearts” (Jer. 31:33). Why should we think it strange for God to assure us by manifesting to us, in our very lives, the sanctifying impact of his grace?
Assurance, like every part of the Gospel, is a heavenly mystery, beyond the reach of the natural man. It is Spirit-discerned, and folly to those who are perishing. Moreover, abusus non tollit usum (abuse does not destroy proper use): we cannot argue from the shipwrecks of faith which those who misunderstand this doctrine have made to its invalidity. Let us instead, without wavering or fearing, lift up our drooping hands and strengthen our weak knees, so that what is lame may not be put out of joint but rather healed, in order to strive for peace and the holiness without which no one will see the Lord. Let us be grateful for receiving a kingdom that cannot be shaken, and thus let us offer to God acceptable worship, with reverence and awe, for our God is a consuming fire (Heb. 12:12ff).