From: John 19:31-37
Jesus' Side Is Pierced
 Since it was the day of Preparation, in order to prevent the bodies from remaining on the cross of the sabbath (for that sabbath was a high day), the Jews asked Pilate that their legs might be broken, and that they might be taken away.  So the soldiers came and broke the legs of the first, and of the other who had been crucified with him;  but when they came to Jesus and saw that he was already dead, they did not break his legs.  But 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 tells the truth--that you also may believe.  For these things took place that the scripture might be fulfilled, "Not a bone of him shall be broken."  And again another scripture says, "They shall look on him whom they have pierced."
31-33. Jesus dies on the Preparation day of the Passover--the Parasceve--that is, the eve, when the paschal lambs were officially sacrificed in the Temple. By stressing this, the evangelist implies that Christ's sacrifice took the place of the sacrifices of the Old Law and inaugurated the New Alliance in his blood (cf. Heb 9:12).
The Law of Moses required that the bodies should be taken down before nightfall (Deut 21:22-23); this is why Pilate is asked to have their legs broken, to bring on death and allow them to be buried before it gets dark, particularly since the next day is the feast of the Passover.
On the date of Jesus' death see "The Dates of the Life of our Lord Jesus Christ" in the "The Navarre Bible: St. Mark", pp. 48ff.
34. The outflow of blood and water has a natural explanation. Probably the water was an accumulation of liquid in the lungs due to Jesus' intense sufferings.
As on other occasions, the historical events narrated in the fourth Gospel are laden with meaning. St. Augustine and Christian tradition see the sacraments and the Church itself flowing from Jesus' open side: "Here was opened wide the door of life, from which the sacraments of the Church have flowed out, without which there is no entering in unto life which is true life. [...] Here the second Adam with bowed head slept upon the cross, that thence a wife might be formed of him, flowing from his side while he slept. O death, by which the dead come back to life! is there anything purer than this blood, any wound more healing!" (St. Augustine, "In Ioann. Evang., 120, 2).
The Second Vatican Council, for its part, teaches: "The Church--that is, the kingdom of Christ--already present in mystery, grows visibly through the power of God in the world. The origin and growth of the Church are symbolized by the blood and water which flowed from the open side of the crucified Jesus" (Vatican II, "Lumen Gentium", 3).
"Jesus on the cross, with his heart overflowing with love for men, is such an eloquent commentary on the value of people and things that words only get in the way. People, their happiness and their life, are so important that the very Son of God gave himself to redeem and cleanse and raise them up" ([St] J. Escriva, "Christ Is Passing By", 165).
35. St John's Gospel presents itself as a truthful witness of the events of our Lord's life and of their spiritual and doctrinal significance. From the words of John the Baptist at the outset of Jesus' public ministry (1:19) to the final paragraph of the Gospel (21:24-25), everything forms part of a testimony to the sublime phenomenon of the Word of Life made Man. Here the evangelist explicitly states that he was an eyewitness (cf. also Jn 20:30-31; 1 Jn 1:1-3).
36. This question refers to the precept of the Law that no bone of the paschal lamb should be broken (cf. Ex 12:46): again St John's Gospel is telling us that Jesus is the true paschal Lamb who takes away the sins of the world (cf. Jn 1:29).
37. The account of the Passion concludes with quotation from Zechariah (12:10) foretelling the salvation resulting from the mysterious suffering and death of a redeemer. The evangelist thereby evokes the salvation wrought by Jesus Christ who, nailed to the Cross, has fulfilled God's promise of redemption (cf. Jn 12:32). Everyone who looks upon him with faith receives the effects of his Passion. Thus, the good thief, looking at Christ on the cross, recognized his kingship, placed his truth in him and received the promise of heaven (cf. Lk 23:42-43).
In the liturgy of Good Friday the Church invites us to contemplate and adore the cross: "Behold the wood of the Cross, on which was nailed the salvation of the world", and from the earliest times of the Church the Crucifix has been the sign reminding Christians of the supreme point of Christ's love, when he died on the Cross and freed us from eternal death.
"Your Crucifix.--As a Christian, you should always carry your Crucifix with you. And place it on your desk. And kiss it before going to bed and when you wake up: and when your poor body rebels against your soul, kiss it again" ([St] J. Escriva, "The Way", 302).
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.