ISB ~ 1 John 3 v6

does not sin:The point is not that sinless perfection is required to call oneself a Christian, but that true believers refuse to lead lives dominated by sin. Instead, they strive to break free from godless habits, and, whenever necessary, they seek God’s mercy through confession (1:9; 2:1).

This focus on the moral life leads John into a discussion about family likeness:the children of the devil act like the devil, while the children of God imitate the love of God (3:7-10).

• Even now we are the children of God because we possess the firstfruits of the Spirit. However, since we are not yet fully saved or renewed, we are also children of the world. This explains why we are still able to sin. Insofar as we are sons of God by the regenerating Spirit, we cannot commit sin; and yet, if we say that we have no sin, we are only deceiving ourselves (St. Augustine, On the Merits and Remission of Sins 2, 10).