I get the question from Christians a lot: “How can I know for sure that I’m saved?” So often, in fact, that I wrote a book addressing it: Stop Asking Jesus Into Your Heart (which you can pre-order here). I struggled with the question a lot myself until someone pointed me to passage from 1 John that helped open my eyes. In 1 John 5:13–18, John identifies 2 ways that we can be sure of our salvation.
1. We have placed our hopes for heaven entirely on Jesus. (1 John 5:13)
“I write these things to you,” John says, “who believe in the name of the Son of God.” It’s so simple that we’re liable to miss it, but assurance comes from believing in Jesus. This is the gospel: when we trust in his name, we cease striving to earn heaven by drawing upon our own moral bank account; instead, we withdraw on his righteous account in our place.
The gospel, by its very nature, produces assurance. Because the gospel proclaims “Jesus in my place,” my assurance does not depend on how well or how much I have done. It depends on whether or not I rest in his finished work. So the question is not, “Can I remember praying a prayer?” or “Was my conversion experience really emotional?” The important question is, “Are you currently resting on Jesus as the payment for your sin?”
A lot of Christians get caught up looking for assurance to a prayer they prayed 2 years, 5 years, or 30 years ago. But John does not say, “I write these things to you who prayed the sinner’s prayer.” He writes to those who believe. The point is not the prayer you prayed, but the present posture you are in.
2. You have a new nature. (vv. 16–18)
If you have been born of God you have been given a new nature. And that comes with new desires. So you do not “keep on sinning,” as John writes, because you have new desires. As an earthy way to think about this, you might imagine some vomit on the ground. None of us would require a list of rules keeping us from eating it. Why? Because we find it disgusting. Now, a dog has a totally different nature, with different desires. A dog would find that vomit as appetizing as we find it disgusting.
This is how God changes us: not by browbeating us with rules, but by giving us a new heart. You no longer love dishonesty and hatefulness and immorality like you used to. You do not avoid them because of threats from God, but because these things start to make you sick.
Of course, this does not mean that you become immediately perfect, or that you no longer struggle with sin. But you stop engaging in sin willfully and defiantly. You cannot love God and love the things that grieve him. You cannot have a mouth that sings praise to Jesus with a life that openly crucifies him. It is not your mouth that best reflects your love for God; it is your life.
And when you do start to go back toward your sin—which we all do!—Jesus protects you and renews you (v. 18). In fact, one of the signs that your salvation is genuine is that even though you fall, you never permanently fall away. God brings you back, again and again. As Proverbs says, “The righteous man falls seven times, and rises again” (Prov 24:16).
Your new nature is not demonstrated by never falling, but by what you do when you fall. Salvation does not means sinless perfection, but it does mean a new direction.