The chief priests of the Jews wanted Pilate to change the title placed on the cross. They did not want Our Lord named as the “King of the Jews,” but as a pretender to that title. Pilate frustrated them, “What I have written, I have written.” If the Lord is to be crucified, though innocent and mocked by his soldiers, then Pilate will at least allow Him the dignity of the title for which He is executed. Pilate does not come off well in these accounts, but he is portrayed as being more decent than the priests.
A bit later they will petition Pilate to break the Lord’s legs so that the Law might be observed. They didn’t want the dead bodies of criminals mucking up their Passover. They were not asking for mercy for Jesus, but further humiliation for their own convenience. Pilate was willing to allow it. It seems in his case that it was a small mercy, but the soldiers, once they discovered that Jesus was already dead, would not do it. They had tortured and mocked and killed Him, but they would not desecrate His body.
Earlier these same soldiers had decided not to tear His tunic and thus had fulfilled the Scriptures, when they decided not to break His bones, again they fulfilled the Scriptures.
The greatest moment for the soldiers is yet to come, though.
John’s Gospel presents a soldier piercing Our Lord’s side and setting loose a flood of blood and water. Some have speculated that this has no more significance than to demonstrate to us that Jesus was really dead. Others have searched hard to try and understand what sort of a condition would cause a corpse to emit blood and a fluid that looks like water. Clearly, however, John is not in the least bit interested in that information. He writes:
One of the soldiers pierced his side with a spear, and at once there came out blood and water. He who saw it has borne witness—his testimony is true, and he knows that he is telling the truth—that you also may believe.
Immediately upon relating this event, John assures us that he himself saw it and that is testimony is true. The point here is that in the flow of blood and water something wonderful, perhaps even miraculous has happened.
Some have suggested that John is drawing a parallel to Gen 2:21–22:
The Lord God caused a deep sleep to fall upon Adam, and while he slept took one of his ribs and closed up its place with flesh. And the rib that the Lord God had taken from the man he made into a woman and brought her to the man.
Eve was born from the first Adam’s side. Without her, he was incomplete. John wants to connect the birth of the Church in the death of the Messiah to the birth of Eve. The Christ awakes on Easter and the Spirit brings His Bride to Him, the new Eve, the mother of all the living.
There are other Old Testament passages this might invoke. The Suffering Servant of Isaiah 53 pours out His soul to death. Water flows from the Rock that follows the Israelites in the desert and St. Paul tells us that Rock is Christ. In Ezekiel 47 there are image of water flowing from Jerusalem and in John 7:38 Jesus says living water flows from within Him. At that point, John interrupted with a theological explanation.
In John 7:37–38 Jesus cited a Scripture passage seemingly in reference to himself: “From within him shall flow rivers of living water.” There the evangelist interrupted to explain that Jesus was referring to the Spirit which those who believed in him were to receive, for as yet there was no Spirit since Jesus had not been glorified. In Jesus’ death we now have the hour of his glorification as he has been lifted up on the cross in return to the Father (12:23–24, 28–32; 13:1; 17:1, 10–11). That death is signified by the blood, and the promised Spirit flowing from within him is signified by the water. This interpretation is not contradictory to the idea that Jesus gave over his Spirit to those at the cross in 19:30, but is another aspect of a multifaceted Spirit-giving through the death, resurrection, and ascension of Jesus. (Note that in each case the Spirit comes from Jesus and thus is the Spirit of Jesus.) At the cross his mother and the disciple whom he loved represented the forebears of the Johannine community—a community of the specially beloved who had already come into existence before he died and were the first to receive the Spirit. Now that he has been lifted up in death he is drawing all to himself (12:32), and all those who believe in him shall receive the Spirit (7:39). The same OT passages that were background for the flow of living water from within him in John 7:38 (Num 20:11; Ps 78:15–16; Ezek 47:1; see BGJ 1.321–23) would have been influential in John 19:34b. And granted the importance of Zech 9–14 in the PN, one might single out Zech 13:1: “On that day a fountain shall be opened for the House of David and for the inhabitants of Jerusalem, for the removal of sin and impurity”; and Zech 12:10: “I will pour out on the House of David and on the inhabitants of Jerusalem a spirit of pity and compassion” (see below under 19:37 for further use of this passage).
I began this discussion of the flow of blood and water by pointing to the functional equivalence of John 19:34 and Mark 15:39 in that each features a Roman soldier in an episode that interprets Jesus’ death. We may add that each Gospel passage hints at the wide salvific effect of that death, Mark by having a Gentile confess Jesus, and John by fulfilling Jesus’ promise to draw all to himself through the pouring out of the Spirit to all believers. Yet Mark’s centurion commented on the death christologically, while John’s soldier remains silent. The functional equivalent of Mark’s interpreting centurion is John’s testifying eyewitness in the next verse, to which we now turn.
This strong attestation of the death of Jesus in John was not for apologetics (to prove that Jesus rose from the dead) but for christology: Even from his dead body life-giving elements will come forth (symbolized by blood and water).
 Raymond E. Brown, The Death of the Messiah, Volume 1 and 2: From Gethsemane to the Grave, a Commentary on the Passion Narratives in the Four Gospels (New York; London: Yale University Press, 1994), 1178-82.
 Raymond E. Brown, The Death of the Messiah, Volume 1 and 2: From Gethsemane to the Grave, a Commentary on the Passion Narratives in the Four Gospels (New York; London: Yale University Press, 1994), 1176-77.