¹ tn The translation of καί (kai) at the beginning of 2:3 is important for understanding the argument, because a similar καί occurs at the beginning of 1:5. The use here is not just a simple continuative or connective use, but has more of a resumptive force, pointing back to the previous use in 1:5.

sn Now. The author, after discussing three claims of the opponents in 1:6, 8, and 10 and putting forward three counterclaims of his own in 1:7, 1:9, and 2:1, now returns to the theme of “God as light” introduced in 1:5. The author will now discuss how a Christian may have assurance that he or she has come to know the God who is light, again by contrast with the opponents who make the same profession of knowing God, but lack the reality of such knowledge, as their behavior makes clear.

² tn Grk “know him.” (1) Many take the third person pronoun αὐτον (auton) to refer to Jesus Christ, since he is mentioned in 2:1 and the pronoun αὐτός (autos) at the beginning of 2:2 clearly refers to him. But (2) it is more likely that God is the referent here, since (a) the assurance the author is discussing here is assurance that one has come to know God (all the claims of the opponents in 1:5-2:11 concern knowing and having fellowship with the God who is light); (b) when Jesus Christ is explicitly mentioned as an example to follow in 1 John 2:6, the pronoun ἐκεῖνος (ekeinos) is used to distinguish this from previous references with αὐτός; (c) the καί (kai) which begins 2:3 is parallel to the καί which begins 1:5, suggesting that the author is now returning to the discussion of God who is light, a theme introduced in 1:5. The author will now discuss how a Christian may have assurance that he or she has come to know the God who is light.

³ tn Once more there is the familiar difficulty of determining whether the phrase refers (1) to what precedes or (2) to what follows. Here, because ἐν τούτῳ (en toutw) is followed by a clause introduced by ὅταν (Jotan) which appears to be related, it is best to understand ἐν τούτῳ as referring to what follows. The following ὅταν clause is epexegetical to ἐν τούτῳ, explaining how we know that we love God’s children: “by this we know that we love God’s children, whenever we love God and keep his commandments.”