Peter ostensibly makes the same point in the first chapter of his second epistle. Follow his argument with me. First, he greets the church with the assured blessing of God’s multiplied grace and peace in Christ (2 Peter 1:2), confident that God Himself has given us all the resources we need for life and godliness (v. 3). Using these resources, the Christian is able both to escape the world and its corrupting influence, and to become more and more like God (v. 4). As a result, Peter urges his hearers to put on an expansive list of Christian virtues (vv. 5–7). These virtues are necessary if we are to live fruitful lives in God’s service (vv. 8–10). It is by making a practice of such a lifestyle that we make our calling and election sure (v. 10). This is the way to enter into eternity with full assurance (v. 11).
So, do you see that the Bible clearly teaches that making our calling and election sure is the everyday duty of every faithful Christian? And we fulfill this duty by turning from sin to Christ. True assurance will never be found going in the opposite direction.
Is this not why Paul warned the Roman church, “If you live according to the flesh you will die” (Rom. 8:13)? Commenting on these verses, John Murray said, “Here is an inevitable and inviolable sequence, a sequence which God himself does not and cannot violate.” So, no matter how confident you or I might be of our election, if we live according to the flesh, we will die in hell forever. The same logic undergirds Paul’s repeated warning for us to put off the deeds of the flesh, for “those who do such things will not inherit the kingdom of God” (Gal. 5:21; see 1 Cor. 6:9).
Not even Paul’s great understudy, Timothy, is immune from the sharp edge of this teaching: “This charge I entrust to you, Timothy, my child, in accordance with the prophecies previously made about you, that by them you may wage the good warfare, holding faith and a good conscience. By rejecting this, some have made shipwreck of their faith, among whom are Hymenaeus and Alexander” (1 Tim. 1:18–20). Paul is clearly warning Timothy here not to follow these men’s example. If he does, following God’s inevitable and inviolable sequence, he can expect to share their fate (1 Tim. 1:20).
For this reason, when I am dealing with a professed Christian who lacks assurance of their salvation, once I have made sure they understand the gospel, I try to ensure that they are living it out in a life of repentance and faith. For in my experience as a pastor, when I find a Christian who really struggles with assurance, it is almost always because they are embracing a life-controlling, conscience-defiling, presumptuous sin (Ps. 19:13). In such cases, for true assurance to start, this pattern of disobedience must stop.
Addressing the age-old problem of mental adultery, wasn’t this the very point Jesus made in His famous Sermon on the Mount (Matt. 5:27–29)? “If your right eye causes you to sin, tear it out and throw it away. For it is better that you lose one of your members than that your whole body be thrown into hell.” Do these words not clearly teach that, from the perspective of the Lord Christ, sanctification is a life and death matter. Before the chickens come home to roost, and they will, the soul enslaved to sexual sin (or for that matter any other sin) faces a simple choice: Lose your lust or lose your soul. John Owen said as much in his most famous quip: “Be killing sin, or sin will be killing you”—killing your soul, killing your assurance of God’s love, and killing your certainty that when you come to die, you will go to heaven.
Perhaps the Holy Spirit has brought these words home to your heart. As the prophet spoke to King David after his adultery with Bathsheba, your conscience is pointing its accusing finger, exclaiming, “You are the man!” (2 Sam. 12:7). Take comfort and run to the Savior. He stands as ready as ever to rescue, redeem, and forgive you. His promise, “Whoever comes to me I will never cast out,” is as good for you as it is for any (John 6:37). Anyone who comes, He will take in. And what He would do for any, He will do for you. Come to Jesus, and you will find in Him more than enough grace to subdue your sins, trampling them under His feet, and casting them into the depths of the sea (Mic. 7:18–20). Come to Jesus. You have a heaven to win, a hell to lose, and not a moment to waste! Of that, you can be certain.