John 19:34

Pierced his side] This was done to make sure of His death, and was a common practice at executions. The act was providentially ordered, that it might be made evident that the Resurrection was a resuscitation after a real death, not a mere recovery from a death-like stupor. Blood and water] No satisfactory medical explanation of this phenomenon has been given, though it has been suggested that the death of Christ was due to rupture of the heart consequent upon acute mental sufferings, and that thereupon the cavities of the heart became filled with a watery serum, which flowed out when Christ's side was pierced. The evangelist himself seems to have regarded the strange phenomenon as a miracle; he certainly saw in it a deep mystical significance, for which see on 1 John 5:6.