1 John 5:6

Jesus Christ is the one who came by water and blood – not by the water only, but by the water and the blood. And the Spirit is the one who testifies, because ¹  the Spirit is the truth.

Le 17:11; Isa 45:3,4; Eze 36:25; Zec 9:11; Mt 26:28; Mr 14:24; Lu 22:20; Joh 1:31-33; Joh 3:5; Joh 4:10,14; Joh 6:55; Joh 7:38,39; Joh 14:6; Joh 14:17; Joh 15:26; Joh 16:13; Joh 19:34,35; Ac 8:36; Ro 3:25; Eph 1:7; Eph 5:25-27; Col 1:4; 1Ti 3:16; Tit 3:5; Heb 9:7,14; Heb 10:29; Heb 12:24; Heb 13:20; 1Pe 1:2; 1Pe 3:21; 1Jo 1:7; 1Jo 4:10; 1Jo 5:7,8; Re 1:5; Re 5:9; Re 7:14

¹ 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.”