Expositor's Bible Commentary Commentary 1 John 3:15

"Whosoever hateth his brother is a murderer: and ye know that no murderer hath eternal life abiding in him." — 1 John 3:15 (ASV)

Here John links hatred with murder (cf. Matthew 5:21–22). In the heart there is no difference; to hate is to despise, and murder is the fulfillment of that attitude. Cain, by murdering his brother, was cut off from the covenant community. So no murderer is within the community, nor anyone who “hates his brother.” Such a person has no life of God and no fellowship with the faithful.