“… one of the soldiers pierced Jesus’ side with a spear, bringing a sudden flow of blood and water” (John 19:34).
This small but graphic detail of the crucifixion of Jesus carries more meaning than we might presume, and there are both historical and scriptural reasons why we need to understand it.
John’s account makes it clear that the Roman soldiers wanted to make sure the crucified individuals did not continue alive into the Sabbath day. When they came to Jesus, they found him apparently already dead – so one of the soldiers pierced his side, doubtless with an intent to puncture his heart, to make sure he was no longer alive (John 19:31-33).
John’s account of the event is important in our knowing that Jesus was truly dead and that the imaginative reconstructions of those who surmise Jesus was perhaps not killed by his crucifixion are not based on fact. But what John records is important in another way.
First, we should understand what the blood and water were. Anyone mercilessly whipped by “flogging,” as Jesus was, could go into hypovolemic shock caused by loss of blood. The medical symptoms of this condition are exactly consistent with John’s description of the crucifixion. For example, the victim could collapse due to low blood pressure (John 19:17); the kidneys could shut down and the victim would experience extreme thirst as the body could not replenish lost fluids (John 19:28).
There is also another symptom of the body’s natural reaction to the extensive laceration by flogging that we should understand. The hypovolemic shock Jesus inevitably experienced would cause sustained rapid heartbeat and fluid would gather within the pericardium, the membrane forming a sack around the heart. This gathering of fluid, called “pericardial effusion,” explains why, after the soldier thrust a spear through Jesus’ side to reach his heart, blood and water came out as John recorded (John 19:34).
But the significance of this careful recording by John goes beyond establishing that Jesus was, in fact, dead. The Book of Hebrews tells us, regarding the establishment of the Sinai covenant between God and ancient Israel:
“Therefore even the first covenant was not inaugurated without blood. For when every commandment had been spoken by Moses to all the people according to the Law, he took the blood of the calves and the goats, with water and scarlet wool and hyssop, and sprinkled both the book itself and all the people…” (Hebrews 9:15-19).
The scarlet wool and hyssop branches were not sprinkled on the congregation. They were the instruments – symbolic of sacrifice and cleansing respectively - used to sprinkle the blood and water on the people. It was the sprinkling of the blood and water that ratified the Old Covenant. In the death of Jesus, the blood and water that flowed from his side were the manner in which the new covenant was inaugurated – a covenant made not just with one nation, but with all of humanity.