The reason John gives for why a Christian cannot continue to persist in sin is that “God’s nature [literally, ‘seed’] abides in him.” This can be taken in a variety of ways, but it should probably be taken as a reference to the very nature of God abiding in the Christian, as the RSV and some other modern versions do.
Herein lies the explanation of John’s initial test and the reason behind it. If a person has truly been born of God, then something quite radical has happened to him. He has received a new nature and is therefore and for that very reason launched on a new course. The course is a course in holiness. If he does not go on in holiness, this indicates that he has never in plain fact been born again. On the other hand, if he does go on, he can be encouraged by this and take confidence. It is probably this test more than any other that enabled the apostle to dismiss the Gnostic teachers as unbelievers.
John’s final statements, both for verses 4-7 and for verses 8-10, are in the nature of an appeal for sound thinking. They provide a conclusion. “Little children, let no man deceive you: he that doeth righteousness is righteous, even as he is righteous. . . . In this the children of God are manifest, and the children of the devil: whosoever doeth not righteousness is not of God, neither he that loveth not his brother.”
The Gnostics with their keen minds and sophistry were capable, not only of making their own sinful conduct seem right, but also of confusing the Christians in regard to who was and who was not God’s child. But John does not want anyone to be confused. Therefore he draws the issue in as black and white tones as possible. To begin with, he indicates that in spiritual terms there are only two groups of people: those who are God’s children and those who are not. And he indicates by his very language that it is only by a new birth that one enters the former of the two groups. The issue is therefore not one of knowledge, as the Gnostics affirmed. Nor is it one of progression along a certain religious scale. One does not grow into Christianity. From the divine side, one enters it by rebirth. From the human side, one enters it through believing on Jesus Christ as Savior and Lord. Nothing must cloud these facts. Indeed, they must be stated in the sharpest of terms.
Here is a word particularly suited to our day. Today, as the result of the widespread impact of Christianity upon western life and culture, many claim to be Christians who are not and who therefore obviously do not have the evidences of the new birth in their lives. They think they are Christian. But this is largely a negative conviction. It is because they are not Muslims or Jews or atheists, not because there has been a genuine work of God in their lives with its inevitable consequences. To all such John sounds a somber warning. “Whoever does not do right is not of God! Let no man deceive you!” It is a warning for all who have not been born again to turn from all forms of sin and seek the Savior.