What does 1 John 3:8 mean?

Again as in verses 6—7, John emphasizes that those who live in consistent, habitual sin have no fellowship with Christ. In fact, John clearly states that all sin is from the Devil; it can never be from a relationship with Christ. All sin, in all forms, is from Satan. This verse is frequently interpreted as a warning to unbelievers, whose lives are marked with habitual, unrepentant sin. The specific context, however, is to Christians. As Paul does in Romans and Galatians, John seems to be refuting the claim that the gospel gives Christians a license to sin.

Christians are not supposed to submit to our sin natures. John points out that Jesus appeared to destroy the Devil's works. This teaching closely reflects Hebrews 2:14: "Since therefore the children share in flesh and blood, he himself likewise partook of the same things, that through death he might destroy the one who has the power of death, that is, the devil." Believers are to resist the devil (James 4:7), who will eventually receive his proper judgment (Revelation 20:10).