What does 1 John 3:9 mean?

John continues his teaching on the topic of those who continue in sin. This is most often interpreted as a warning that such people are not believers. While this seems to agree with the general sense of Scripture, John's advice here is actually being targeted specifically at believers. In particular, that there is no excuse for sin in the life of a believer. Grace is a not a license to sin. Those who sin without remorse, conviction, or change have no relationship with Christ whatsoever. But even a saved Christian has to choose good over evil.

In this verse, the emphasis is on the one "born of God." God lives in the believer and the believer can therefore no longer live the same life as prior to becoming God's child. Though believers continue to sin, they will be changed more into the likeness of Christ. God's children are expected to reflect his characteristics to some degree. Again, the emphasis is not on perfection, but likeness. An unchanged person is not a true believer. A true believer cannot help but live differently because God lives within them.