The author is alluding to the rule given in Gen 9.6, “he that sheds the blood of a man, for that man his blood shall be shed” (New English Bible). He applies this rule figuratively to the new life of the Christian. The verse probably serves to explain verse 14; hence “for everyone who hates…” (New English Bible). Most versions, however, do not specify a connection.

Who hates his brother, see comments on 2.9.

Is a murderer is to be taken as a metaphorical application of verses 11-12. The clause serves to make clear that hatred is close to murder, being the first step toward it and belonging to the same moral category.

Murderer: in form the Greek term, literally “man-killer,” is not related to the verb used in verse 12. In meaning it is the more generic of the two in that it does not suggest violent passion. If the word is to be rendered by a phrase, one may say ‘one who kills people.’

You know: some versions give a less prominent position to this phrase by subordinating it; for example, “no murderer, as you know, has eternal life” (New English Bible). This has the advantage of contrasting more closely and directly the preceding and the present clause, which say who is a murderer, and what a murderer cannot have, respectively.

No murderer has eternal life abiding in him: for the construction “to have eternal life” compare comments on “to have … sin” in 1.8. The expression means that one is in a condition characterized as, and influenced by, eternal life or, otherwise stated, that one has the source and principle of eternal life in oneself. The present tense of “to have” has durative force. The participial phrase abiding in him does not add a new fact but serves to emphasize the concept of duration.

Possible restructurings and adjustments of the clause are ‘a murderer cannot be and remain in possession of eternal/true life,’ ‘eternal/true life cannot be and continue to be dwelling in a murderer,’ ‘to kill people and to live for the age to come can never go together.’ For eternal life see comments on 1.1-2; for abiding in see comments on 2.14.

Quoted with permission from Haas, C., de Jonge, M. and Swellengrebel, J.L. A Handbook on The First Letter of John. (UBS Handbook Series). New York: UBS, 1972. For this and other handbooks for translators see here .