I John 3:11

the message--"announcement," as of something good; not a mere command, as the law. The Gospel message of Him who loved us, announced by His servants, is, that we love the brethren; not here all mankind, but those who are our brethren in Christ, children of the same family of God, of whom we have been born anew.

The apostle, having intimated that one mark of the devil's children is hatred of the brethren, takes occasion thence, I. To recommend fraternal Christian love, and that from the excellence, or antiquity, or primariness of the injunction relating thereto: And this is the message (the errand or charge) which you heard from the beginning (this came among the principal parts of practical Christianity), that we should love one another, Jo1 3:11. We should love the Lord Jesus, and value his love, and consequently love all the objects of it, and thereupon all our brethren in Christ. II. To dissuade from what is contrary thereto, all ill-will towards the brethren, and that by the example of Cain. His envy and malignity should deter us from harbouring the like passion, and that upon these accounts: - 1. It showed that he was as the first-born of the serpent's seed; even he, the eldest son of the first man, was of the wicked one. He imitated and resembled the first wicked one, the devil. 2. His ill-will had no restraint; it proceeded so far as to contrive and accomplish murder, and that of a near relation, and that in the beginning of the world, when there were but few to replenish it. He slew his brother, Jo1 3:12. Sin, indulged, knows no bound. And, 3. It proceeded so far, and had in it so much of the devil, that he murdered his brother for religion's sake. He was vexed with the superiority of Abel's service, and envied him the favour and acceptance he had with God. And for these he martyred his brother. And wherefore slew he him? Because his own works were evil, and his brother's righteous, Jo1 3:12. Ill-will will teach us to hate and revenge what we should admire and imitate. And then, III. To infer that it is no wonder that good men are so served now: Marvel not, my brethren…

3:11-22 John now focuses on the believers’ need to love one another (see John 13:34).