What We Know
"John concludes this section with three bold statements about Christian certainty. Verses 18, 19, and 20 each begin with the same statement, “We know” (Gk. oidamen; cf. 3:2, 14), which gives the verses a rhythmic cadence. And in each case, the verses sound themes that have been dear to John’s heart from the first chapter. The first addresses the ongoing righteousness of God’s children; the second speaks of the fallenness of the world; the third gives the hope that is in Christ as we live in this world. Sanctification, disintegration, and redemptive hope are John’s final words to his readers.
John’s earlier reference to sin (vv. 16–17) inspires a sweeping statement about Christians: They do not sin. The NIV translates “continue to sin” in order to reflect the present tense of the Greek verb. The subject of Christian perfection appeared earlier in 3:6–9; there we explained that even though John seems to be saying that Christians never sin (or cannot sin, 3:9), this hardly fits our Christian experience and does not agree with the teaching elsewhere in the letter about sin (1:7–10; 2:1). The Greek present tense suggests ongoing activity; hence, Christians (in John’s view) do not have the habit of sinning. Christians do not “live in sin.”
But more must be said. John may have in mind the distinction already raised in verses 16–17, that Christians do not engage in “sin that leads to death,” namely, intentional, willful acts against God. Why? Because all people who are genuinely Christians have been “born of God.”9 There are no exceptions. Furthermore, Christ himself sustains and protects them from the evil one (v. 18b). Therefore, Christians do not engage in this sort of sustained, willful repudiation of God. Jesus’ protection of his followers is a regular Johannine theme (John 10:7–17; 17:12), and John here affirms that the Christian’s plight in the world is not solitary. The quest for righteousness is supported and sustained by Jesus himself. Believers keep Jesus’ word because Jesus keeps them.
But we also know more (v. 19). This is John’s second bold affirmation. The sustenance and protection of Jesus are essential because the world lies (NIV, “is under the control of”) in the grip of Satan. John’s imagery is striking. The world is not under siege by Satan; it hardly struggles against him at all. The world rests in Satan’s arms. John’s dualistic outlook is once again drawing sharp boundaries between church and world, light and darkness, God and the evil one. Christians reside in the rival camp to Satan, but our security is assured because Jesus resides there with us. The world is used to Satan’s embrace, but Christians cannot be held by him.
Finally, John makes clear our hope. If the world is experiencing disintegration and there are many aligned with the forces of evil, what hope is there for us in the world? John’s answer (v. 20) is that Jesus Christ has penetrated the world; he has worked as saboteur, undermining the systems of the world and reversing its possibilities. Note that here John describes the work of Christ as bringing knowledge (he “has given us understanding, so that we may know …”), but this should not be seen as a type of Gnostic enlightenment—the very thing to which John is opposed! Christian knowledge is focused on genuine reality, things that happened in history. Thus in verse 20 John does not say we merely know truth (Gk. aletheia); rather, we know “him who is true [or real]” (Gk. alethinon). John uses an adjective rather than the usual noun to underscore that Christian certainty is not about abstract reason or inspired enlightenment, but about God, the real God, “him who is true,” the only true God (cf. 1 Sam. 3:7; Jer. 24:7; 31:34; John 1:9; 15:1; Rev. 3:7).
To be in the truth (v. 20b), then, is not just about being right, but about sharing in true reality (as opposed to falsehood). John’s final thought is undoubtedly the most important. The NIV takes verse 20a as referring to Jesus Christ (“He is the true God and eternal life”), and though interpreters differ, “he” can fully refer to the Son rather than the Father. It is fitting that John’s letter ends here. Throughout his writing he has promoted and defended the full divinity of Christ. To lose this one conviction is to miss not just Jesus but God himself."