Little children, let no one lead you astray. He who does righteousness is righteous, even as he is righteous.
John cannot find words to express his feelings when he considers the great love God has shown in making sinful people his children. They now think and act according to the nature of their heavenly Father, with the result that unbelievers, who think and act according to the world’s standards, cannot understand them (3:1). God’s children know little about the nature of life in the world to come, but they know at least that in some way they will be like Christ. This is good reason for them to become as much like Christ as possible in their present lives. They should be pure in thought and behaviour as he was (2-3).According to the bold assertions of the false teachers, knowledge is all-important and behaviour does not matter. John contradicts this, pointing out that sin is the breaking of God’s law. Therefore, if people deliberately carry on sinning, they know neither God who gave the law nor Christ who takes away sin. John is not saying that Christians cannot sin (he has already shown the impossibility of this in 1:6-10), but that they do not sin as they like. They may have failures and make mistakes, but they do not sin habitually (4-6).The behaviour of people shows whether they belong to Christ or the devil. They cannot belong to both, as the two are opposed to each other (7-8). If they are true Christians, they will have a divine power within them fighting the devil so that they might not sin. If they sin habitually, it shows that they are not Christians (9-10).