Although we could spend a week on examining Good Friday because there is so much there, lets focus on one aspect of the Day. The Gospel on Good Friday is always from the writing of John. After all, John was there. And only John tells us of the Blood and Water from the Side of Jesus.
“... so they put a sponge full of wine on hyssop and held it to his mouth. When Jesus had received it, he said, “It is finished”; and he bowed his head and gave up his spirit. Since it was the day of Preparation,” “...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 may also believe. For these things took place that scripture might be fulfilled, “Not a bone of him shall be broken.” (Exodus 12:46) (John 19:26-37)
Why does John make a point about the hyssop branch and no broken bones? Because Jesus is the new Passover Lamb. At the time of the Exodus the Jews had to place the blood of an unblemished lamb (no disease or broken bones)on the lintel and doorposts of their home with a hyssop branch. The soldier dips the hyssop branch in wine. The New Passover Lamb will give us His Blood under the appearances of wine in the Holy Eucharist.
Blood and Water from the side of the Temple.
There is more to the story, though. Blood and water coming from the side of Jesus does show that He was dead. But if you were a first century Jew, you would know that over 250,000 lambs were sacrificed from the ninth to the eleventh hour. At the south-western corner (of the altar) there two narrow like nostrils by which the blood that was poured out over the western and southern base used to run down and mingle in the water-channel and flow into the brook Kidron. (Mishnah Middrath 3:2 trans H. Danby)
When John saw this he makes the connection that not only is Jesus the New Pascal Lamb, he is the New Temple. The blood and water flowing out of Jesus is flowing to atone for for our sins and that of the whole world. If his body is the Temple, then where is the altar? The altar is his Sacred Heart. The Love that flows from Jesus is the Water that will Baptize us, and the Blood that will give life to us in the Holy Eucharist. John realized that Redemption of the world has just taken place!