Children, let no one deceive you. The one who does what is right is righteous, just as he is righteous.
John’s tender affection for his readers causes him to remind them of the peril of their situation and to be on guard against those who want to lead them astray by convincing them that the nature of our salvation and Savior do not require holiness; they must stand fast in the truth of our precious gospel (2:24) and continue to follow Christ in the light (1:5-6).
“Children, let no one deceive you”: This imperative commands John’s spiritual children to guard against deception on this point in the same way that soldiers guard against the enemy’s invasion.
The believers that John is writing to are facing an onslaught of false teachers who are actively trying to deceive them:
1 John 2:26 (CSB) — 26 I have written these things to you concerning those who are trying to deceive you.
John commands his spiritual children to close the church door to these deceivers so that they are not allowed to take them captive through their false doctrine. And this command reaches through time and calls on us to close the door to those who preach a gospel of accommodation towards sin in order to “make provision for the flesh” (Rom. 13:14). But in order to fully guard against these false doctrines, they must also grow in their unity of faith in the knowledge of Christ:
Ephesians 4:13–15 (CSB) — 13 until we all reach unity in the faith and in the knowledge of God’s Son, growing into maturity with a stature measured by Christ’s fullness. 14 Then we will no longer be little children, tossed by the waves and blown around by every wind of teaching, by human cunning with cleverness in the techniques of deceit. 15 But speaking the truth in love, let us grow in every way into him who is the head—Christ.
Reaching unity in the faith and in the knowledge of Christ in the maturity of Christ’s fullness is presented by Paul as the means by which the winds and waves of false teaching and deceit will ultimately be stopped.
This command to guard against deception on the point of holiness sets up John’s contrast between the Spirit of Truth and the Spirit of Deception:
1 John 4:6 (CSB) — 6 We are from God. Anyone who knows God listens to us; anyone who is not from God does not listen to us. This is how we know the Spirit of truth and the spirit of deception.
Whoever rejects these doctrines rejects God and has been deceived by the spirit of deception. Whoever embraces these doctrines and lives by them knows the Spirit of Truth and comes from God.
“The one who does what is right is righteous”: John carefully calls out the subject of this deception as that which centers around the false notion that one could “be” righteous without necessarily bothering to “practice” righteousness. John states in clear terms that only the person who lives in righteousness is righteous.
John is using the literary device of “contrast” to define the reality of what it means to be a child of God by addressing this idea from two contrasting vantage points. From the negative perspective, it is impossible for a Christian to live in a state of sin, while from the positive perspective he says that Christians will live in a state of righteousness.
The present tense participle in this clause makes clear that the test is not the performance of an occasional righteous deed but rather the habitual practice of “righteousness”. Furthermore, “the righteousness” (τὴν δικαιοσύνην) indicates that a very particular kind of righteousness is in view. John means to emphasize the completeness and unity of this righteous quality as being the righteousness that is characteristic of Christ himself. This righteousness is the distinguishing trait of God’s family and is a product of regeneration.