JMNT(i)
12 not [living] like (or: not just as) Cain. He was existing, and continued being, from out of the condition (or: situation; or: one; thing; = influence) causing misery and hard labor (the unprofitable attitude; the worthless mindset; the wicked intent; the toilsome situation; the sorry plight), and so he slaughtered (killed by cutting his jugular vein) his brother. And on what score (or: for what pleasure) did he slaughter him? Because his works (actions) were gushed with misery and hard labor (were wicked or evil; were toilsome; were unprofitable and worthless), but those of his brother [were] ones in accord with the Way pointed out (just ones; righteous ones; fair and equitable ones; rightwised ones).
13 Stop marveling (Cease wondering; Quit being astonished), brothers, if (or: since) the ordered System (world of culture and religion; or: the estranged secular system of governmental control) is constantly hating you (habitually regarding you with ill-will).
14 We ourselves have seen, and thus know (or: are aware), that we have walked together (or: proceeded to change, passing from) out of the Death into the Life, because we are habitually loving the brothers (= fellow believers; [some MSS: our brothers; {or: = our fellow human beings}]). The person not habitually loving [some MSS add: his brothers] continues remaining (dwelling; abiding; staying) within the Death.
15 Everyone constantly hating (or: regarding with ill-will) his brother constantly exists being a person-slayer (a murderer), and has not seen so as to be aware that every person-slayer does not presently have (or: is not continuously holding) life having its source in, or having the quality of, the Age (or: eonian life) presently remaining within him (or: continuously dwelling and abiding in union with him).