Who is Jesus, the son of God? John says, “the one came by water and blood.” This is an obscure answer. Although there are many modern suggestions for what John meant, Karen Jobes suggests the original readers would have understood this allusion because they have firsthand knowledge of the teaching of the ones who have left the church. John only needs to briefly allude to them by means of these obscure words and they would understand what he meant (Jobes, 1, 2, & 3 John, 220).
Including the Spirit, there are three things are in agreement that Jesus is the Son of God. There are two possible allusion to the Gospel of John in these verses. In John 3:5, one cannot see the kingdom of Heaven without being born of water and the Spirit. In John 19:34, when Jesus is pierced water and blood flow from his side. When the soldiers approach Jesus, he is already dead but they confirm this by piercing his side with a spear. As a result, blood and water flow, indicating that the blood was already separating.
The main point of this flow of water and blood was to confirm the death of Jesus. That he was “really dead” is important for the resurrection. The Romans did not take a partially dead man from the cross who could “revive” with a little medical attention. Indeed, Jesus was dead. John may be alluding to Scripture, such as Exodus 17:6, “strike the rock and the water will flow.” Water is the source of life, certainly water from the hand of God in Exodus 17 is a symbol of salvation provided by God. There are many verses which describe God himself as the Rock of Salvation Ps 18:31, for example).
John tells us the soldier who pierced Jesus’ side bears witness this is truly what happened. The beloved disciple also witnesses this piercing, so that John’s claim here in 1 John is “I am an eyewitness of the water and the blood.”
One option but interpreting the water and the blood to take them as a reference to literal water and blood. There are two possibilities here: First, Jesus’s birth and death. Here water refers to the breaking of the water prior to birth and the blood refers to the crucifixion. Similarly, Kruse observes there are ancient Jewish sources describing the human body as composed of two elements, water and blood (Kruse, The Letters of John, 176). However, he does not cite any sources which actually say this. Jesus’s baptism and death. Using the Gospel of John as a guide, the phrase “in water only appears in the Gospel with reference to John’s baptism (John 1:26, 31, 33; Kruse, Epistles of John, 175). This would then refer to Jesus’s whole ministry from baptism through the death on the cross.
A second option is to take the water and the blood as a metaphor relating to something in the Christian life or practice. For example, some church fathers took the water as a reference to water baptism and the blood to the Eucharist (Tertullian, Augustine, Ambrose). Sometimes this “water and blood” was related to John 4 (living water) and John 6 (bread from heaven), both commonly taken as an allusion to the (later) practice of the Eucharist (Calvin and Luther? Find a reference to this). It is likely there are a few commentaries to be cited that see this as an indication of a later date for the letter and reflecting the growing importance of the Eucharist.
The real problem for “blood” as a reference to taking communion is the cup as “the blood of Jesus” is not found in John’s Gospel, and in the synoptic gospels the cup represents the blood which initiates the New Covenant. It is only in later Catholicism the cup is understood as the literal blood of Jesus.
More recently, To Thatcher suggested water is the Holy Spirit and blood refers to the physical death of Jesus on the Cross. This is attractive because the Old Testament often portrays the Holy Spirit in liquid terms, he is “poured out” on God’s people. In addition, Paul’s description of the baptism in the Holy Spirit in 1 Corinthians 12 connects the Spirit with water as well.
So what is the “water and blood”? The first phrase in verse 6 refers to the life and atoning sacrifice of Jesus (from baptism to crucifixion); the second in verse 7 adds the Spirit as a witness since the Spirit applies the atoning sacrifice to the life of the believer.
How does the Spirit, water and the blood agree in their testimony Jesus is the Son of God? The tradition of “two or three witnesses” is based on the Law, Deuteronomy 17:6 and 19:15, for example. Something is made certain by three witnesses. John may have in mind the witness of two at the baptism of Jesus (the Spirit descended on Jesus) and the two witnesses at the cross, the blood and water from the side of Jesus.
Bibliography: Tom Thatcher,“‘Water and Blood’ in Anti-Christ Christianity (1 John 5:6).” SCJ 4 (2001): 235–48; see also his commentary on these verses: “1 John,” “2 John,” “3 John.” Pages 414–538 in The Expositor’s Bible Commentary, vol. 13 (Rev. ed. Edited by Tremper Longman III and David E. Garland. Grand Rapids: Zondervan, 2006); (Ben Witherington, III, “The Waters of Birth: John 3:5 and 1 John 5:6–8,” NTS 35 (1989): 155–58).