Expositor's Bible Commentary Commentary 1 John 3:12

"not as Cain was of the evil one, and slew his brother. And wherefore slew he him? Because his works were evil, and his brother`s righteous." — 1 John 3:12 (ASV)

The mention of Cain points back to 3:8 and reminds us that hatred is also from the beginning. The choice between the children of God and the children of the devil, between hatred and love or life and death, stems from the earliest moment of human existence. It also points to Jn 8:37–47, where some Jewish opponents of Jesus had exhibited the same kind of hatred toward Jesus that Cain expressed toward Abel . There Jesus labels his enemies as people who “belong to your father, the devil... [who was] a murderer from the beginning” .

The sequence of thought in this section is significant. It is not that Cain by murdering his brother became the child of the devil; but, being a child of the devil, his actions were evil and culminated in the murder of his brother. The reason why he “murdered” (lit., “butchered”; GK 5377) him was that his brother’s acts were righteous. Righteousness draws hatred from the devil and hatred from the children of the devil. Darkness cannot tolerate light; immorality, morality; hatred, love; or greed, sacrifice. This is the only direct reference to the OT in this letter.