10 By this it is made clear who take their nature from God and are His children and who take their nature from the devil and are his children: no one who does not practice righteousness [who does not conform to God's will in purpose, thought, and action] is of God; neither is anyone who does not love his brother (his fellow believer in Christ).
11 For this is the message (the announcement) which you have heard from the first, that we should love one another,
12 [And] not be like Cain who [took his nature and got his motivation] from the evil one and slew his brother. And why did he slay him? Because his deeds (activities, works) were wicked and malicious and his brother's were righteous (virtuous).
13 Do not be surprised and wonder, brethren, that the world detests and pursues you with hatred.
14 We know that we have passed over out of death into Life by the fact that we love the brethren (our fellow Christians). He who does not love abides (remains, is held and kept continually) in [spiritual] death.
15 Anyone who hates (abominates, detests) his brother [in Christ] is [at heart] a murderer, and you know that no murderer has eternal life abiding (persevering) within him.
16 By this we come to know (progressively to recognize, to perceive, to understand) the [essential] love: that He laid down His [own] life for us; and we ought to lay [our] lives down for [those who are our] brothers [in Him].