Not as Cain, &c.— The original is expressive; Not like Cain! he was of the wicked one, and murdered his brother: God forbid therefore that we should be like him. To be of the wicked one, is the same thing as being a child of the devil. See 1 John 3:8. In this verse St. John assigns a second reason why Christians should love each other, namely, that otherwise they will be like Cain, and children of the devil. If, instead of evil, in the last clause, our translators had rendered it wicked, the apostle's sense would have appeared more plainly; and the connection between the wicked one, and wicked works, would have been set in a stronger light. Cain's brother being preferred to him, gave rise to jealousy,envy, and hatred, which, at length, settling into the most rancorous malice, hurried him on to fratricide. See on Genesis 4:4 and Hebrews 11:4.
Related Commentaries of 1 John 3:12
1 John 3:12
12 Not as Cain, who was of that wicked one, and slew his brother. And wherefore slew he him? Because his own works were evil, and his brother's righteous.