1 tn Once again there is the problem of determining whether the phrase ἐν τούτῳ (en toutw) refers (1) to what precedes or (2) to what follows. This is the first of 5 uses of the phrase in the present section (4:9, 10, 13, 17; 5:2). In this case (as also in the next two instances) there is a ὅτι (Joti) clause following which is related and which explains (i.e., which is epexegetical to) the phrase ἐν τούτῳ. Thus the meaning here is, “By this the love of God is revealed in us: that God has sent his only Son into the world in order that we might live through him.”
2 tn In terms of syntax the force of the genitive τοῦ θεοῦ (tou qeou) may be (1) objective, (2) subjective, or (3) both. The phrase occurs for the first time in the letter in 2:5. Here in 4:9 the epexegetical ὅτι (Joti) clause which follows makes it clear that this is a subjective genitive, emphasizing God’s love for us rather than our love for God, because it describes God’s action in sending his Son into the world.
3 tn This phrase is best understood as the equivalent of a dative of sphere, but this description does not specify where the love of God is revealed with regard to believers: “in our midst” (i.e., among us) or “within us” (i.e., internally within believers). The latter is probable, because in the context the concept of God’s indwelling of the believer is mentioned in 4:12: “God resides (μένει, menei) in us.”
4 sn Although the word translated one and only (μονογενής, monogenhs) is often rendered “only begotten,” such a translation is misleading, since in English it appears to express a metaphysical relationship. The word in Greek was used of an only child (a son [Luke 7:12, 9:38] or a daughter [Luke 8:42]). It was also used of something unique (only one of its kind) such as the mythological bird called the Phoenix (1 Clement 25:2). From here it passes easily to a description of Isaac (Heb 11:17 and Josephus, Ant. 1.13.1 [1.222]) who was not Abraham’s only son, but was one-of-a-kind because he was the child of the promise. Thus the word means “one-of-a-kind” and is reserved for Jesus alone in the Johannine literature of the NT. While all Christians are children of God (τέκνα θεοῦ, tekna qeou), Jesus is God’s Son in a unique, one-of-a-kind sense. The word is used in this way in all its uses in the Gospel of John (1:14, 18; 3:16, 18).
5 tn This ὅτι (Joti) is best understood (1) as causal. Some have taken it (2) as declarative, giving the content of the Spirit’s testimony: “and the Spirit is the One who testifies that the Spirit is the truth.” This is certainly possible, since a ὅτι clause following the cognate verb μαρτυρέω (marturevw) often gives the content of the testimony (cf. John 1:34; 3:28; 4:39, 44). But in the Gospel of John the Spirit never bears witness on his own behalf, but always on behalf of Jesus (John 15:26, 16:13). There are, in fact, some instances in the Gospel of John where a ὅτι clause following μαρτυρέω is causal (8:14, 15:27), and that is more likely here: “and the Spirit is the One who testifies, because the Spirit is the truth.”