31 Then the Jews, (because it was the parasceve,) that the bodies might not remain on the cross on the sabbath day, (for that was a great sabbath day,) besought Pilate that their legs might be broken, and that they might be taken away.
Theophylact: It was commanded in the Law that the sun should not set on the punishment of anyone; or they were unwilling to appear tormentors and homicides on a feast day.
32 The soldiers therefore came; and they broke the legs of the first, and of the other that was crucified with him. 33 But after they were come to Jesus, when they saw that he was already dead, they did not break his legs. 34 But one of the soldiers with a spear opened his side, and immediately there came out blood and water.
Augustine: The Evangelist has expressed himself cautiously; not struck, or wounded, but opened His side: whereby was opened the gate of life, from whence the sacraments of the Church flowed, without which we cannot enter into that life which is the true life: And forthwith came thereout blood and water. That blood was shed for the remission of sins, that water tempers the cup of salvation. This it was which was prefigured when Noah was commanded to make a door in the side of the ark, by which the animals that were not to perish by the deluge entered; which animals prefigured the Church. To shadow forth this, the woman was made out of the side of the sleeping man; for this second Adam bowed His head, and slept on the cross, that out of that which came therefrom, there might be formed a wife for Him.
35 And he that saw it, hath given testimony, and his testimony is true. And he knoweth that he saith true; that you also may believe.
Theophylact: The water flowing is an irresistible miracle, and therefore the Evangelist adds, And he that saw it bare record.
Chrysostom: As if to say, I did not hear it from others, but saw it with mine own eyes.
36 For these things were done, that the scripture might be fulfilled: You shall not break a bone of him. 37 And again another scripture saith: They shall look on him whom they pierced.
Augustine: A bone of Him shall not be broken, a commandment which applied to the sacrifice of the paschal lamb under the old law [Exod 12:46], which sacrifice foreshadowed our Lord’s. . . . Another Scripture said, They shall look on Him whom they pierced [Zech 12:10], a prophecy which implies that Christ will come in the very flesh in which He was crucified.
Scripture from the Douay-Rheims Bible. Commentary from St. Thomas Aquinas, Catena Aurea, Vol. IV (London: Rivington, 1845).