3:10 children of the devil. It is sobering to read that those who are not “children of God” are “children of the devil;” no middle ground is said to exist. They are also called “children of the wicked one” (Matthew 13:38), “children of disobedience” and “children of wrath” (Ephesians 2:2-3). The identification is twofold: those who do not habitually show works of righteousness, and/or those who do not habitually manifest love for other Christians. It is urgent that each one “must be born again” (John 3:3).
3:12 Cain. John thus confirms the historicity of the record of Cain and Abel (Genesis 4). Note also Matthew 23:35; Hebrews 11:4; 12:24.
3:12 wicked one. Though a child of Adam and Eve, the very first family, Cain was called a child of the devil.
3:14 passed from death unto life. Here is another test for knowing whether we are truly saved, and have “passed from death unto life” (John 5:24). See also I John 2:3,5; 3:24; 5:2,13.
3:14 love the brethren. John gives three characteristics of true love for our brethren: doing righteousness (I John 3:10); willingness to die for them (I John 3:16); willingness to share our possessions with them” (I John 3:17).
3:15 a murderer. Compare Matthew 5:21-22.