1 John 5:7,8

The Water (the Lord's consecrated Life) and the Blood (His sacrificial Death) are testimonies to the Incarnation, but they are insufficient. A third testimony, that of the Spirit, is needed to reveal their significance to us and bring it home to our hearts. Without His enlightenment the wonder and glory of that amazing manifestation will be hidden from us. It will be as unintelligible to us as “mathematics to a Scythian boor, and music to a camel”. τρεῖς οἱ μαρτυροῦντες, masculine though Πνεῦμα, ὕδωρ, and αἷμα are all neuter, because agreeing κατὰ σύνεσιν with τὸ Πνεῦμα a testimony, the more striking because involuntary, to the personality of the Spirit. εἰς τὸ ἕν, “for the one end,” i.e. to bring us to faith in the Incarnation (ὅτι Ἰησοῦς ἐστιν ὁ Υἱὸς τοῦ θεοῦ). This was the end for which St. John wrote his Gospel (John 20:31). There is no reference in the Water and the Blood either to the effusion of blood and water from the Lord's pierced side (John 19:34) or to the two Sacraments.