This message of love to the brethren had been heard by the Christian community from the beginning.  It was part and parcel of the Gospel message that was preached by the apostles.  It is powerfully emphasized by all the inspired New Testament writings.  Love to the brethren is the Christian virtue by which men may know that we are believers in Christ: “By this shall all men know that ye are My disciples, if ye have love one to another.”  Does our Christian love manifest that we are the disciples of Christ?

John sets the contrast to Christian love, by pointing to an Old Testament example, the only time he does so in his three epistles.  Cain was in the family of Adam, and unquestionably professed to be a servant of God.  This we know because he offered a sacrifice to the Lord of the fruits of the ground.  But Cain’s wicked heart soon betrayed itself, when the Lord accepted Abel’s offering and spurned his own.  Instead of repenting of his faithless service, he instead became enraged against his own brother, and ultimately murdered him.  That evil man could not bear that the righteousness of his brother be revealed for all the world to see as a contrast to his own wickedness.  The hatred that was in his heart resulted in murder, and proved him to be a child of the devil.

Cain became to the prototype of the godless worldling.  The ungodly world must forever be in opposition to the people of God, because they are directed by opposite principles, and serve completely different masters.  John points them to the prototype of worldly hatred, and then tells them to not be surprised if they find themselves exposed to worldly hatred and violence, as Abel was.  Our devoted service to God will not only prove our allegiance to Him, it will also expose the true colors of the ungodly world, for darkness hates the presence of light.  Thus the world, which lieth in the wicked one, must hate the godly.  We should not marvel, then, if the world hates us, our principles, our practices, and the Master we serve.  After all, it hated Christ before it hated us.