1 John 3:15

"Every one" includes Christians. Murder is the ultimate outward expression of hatred (cf. Matthew 5:21-22). The key to the statement that concludes this verse is the words "abiding in him." John evidently meant that no Christian whose eternal life (i.e., Jesus Christ; 1 John 1:2) has control of him, who is walking in fellowship with God, will commit murder. Some believers have committed murder, but they were not abiding believers when they did so (cf. John 15:4).