This section explains what it means to live a pure life (3:3). Being part of God's spiritual family requires living a pure life. A life full of sin shows that someone is not truly God's child. Sin is not suitable for the new nature that comes from spiritual birth.
John encourages Christians to do what is right to show they are united to Christ and his righteousness. Children of God do not make a practice of sinning. However, this is different from the kind of “sinlessness” claimed by the false teachers (see 1:5–10 and corresponding study notes).