1 John 2:9

2:9 The one who says he is in the light but still hates ¹  his fellow Christian ²  is still in the darkness.

1 John 3:12

3:12 not like Cain ³  who was of the evil one and brutally ⁴  murdered his brother. And why did he murder him? Because his deeds were evil, but his brother’s were righteous.

1 John 4:21

4:21 And the commandment we have from him is this: that ⁵  the one who loves God should love his fellow Christian ⁶  too.

[2:9]  ¹ tn Grk “the one saying he is in the light and hating his brother.” Here καί (kai) has been translated as “but” because of the contrast present in the two clauses.

[2:9]  ² tn Grk “his brother.” Here the term “brother” means “fellow believer” or “fellow Christian” (cf. BDAG 18 s.v. ἀδελφός 2.a). In the repeated uses of this form of address throughout the letter, it is important to remember that sometimes it refers (1) to genuine Christians (those who have remained faithful to the apostolic eyewitness testimony about who Jesus is, as outlined in the Prologue to the letter, 1:1-4; an example of this usage is 2:10; 3:14, 16), but often it refers (2) to the secessionist opponents whose views the author rejects (examples are found here at 2:9, as well as 2:11; 3:10; 3:15; 3:17; 4:20). Of course, to be technically accurate, in the latter case the reference is really to a “fellow member of the community”; the use of the term “fellow Christian” in the translation no more implies that such an individual is genuinely saved than the literal term “brother” which the author uses for such people. But a translation like “fellow member of the community” or “fellow member of the congregation” is extremely awkward and simply cannot be employed consistently throughout.

[3:12]  ³ sn Since the author states that Cain…was of the evil one (ἐκ τοῦ πονηροῦ, ek tou ponhrou), in the immediate context this imagery serves as an illustration of 3:8a: The person who practices sin is of the devil (ἐκ τοῦ διαβόλου, ek tou diabolou). This is similar to John 8:44, where Jesus told his opponents “you people are from your father the devil…[who] was a murderer from the beginning.” In both Jewish and early Christian writings Cain is a model for those who deliberately disbelieve; Testament of Benjamin 7:5 looks forward to the punishment of those who “are like Cain in the envy and hatred of brothers.” It is not difficult to see why the author of 1 John used Cain here as a model for the opponents in light of their failure to “love the brothers” (see 1 John 3:17).

[3:12]  ⁴ tn For the Greek verb σφάζω (sfazw) L&N 20.72 states, “to slaughter, either animals or persons; in contexts referring to persons, the implication is of violence and mercilessness – ‘to slaughter, to kill.’” As a reflection of this nuance, the translation “brutally murdered” has been used.

[4:21]  ⁵ tn The ἵνα (Jina) clause in 4:21 could be giving (1) the purpose or (2) the result of the commandment mentioned in the first half of the verse, but if it does, the author nowhere specifies what the commandment consists of. It makes better sense to understand this ἵνα clause as (3) epexegetical to the pronoun ταύτην (tauthn) at the beginning of 4:21 and thus explaining what the commandment consists of: “that the one who loves God should love his brother also.”

[4:21]  ⁶ tn See note on the phrase “fellow Christian” in 2:9.