"There flowed from his side water and blood. Beloved, do not
pass over this mystery without thought; it has yet another hidden
meaning, which I will explain to you. I said that water and blood
symbolized baptism and the holy eucharist. From these two sacraments the
Church is born: from baptism, the cleansing water that gives rebirth and renewal through the Holy Spirit,
and from the holy eucharist. Since the symbols of baptism and the
eucharist flowed from his side, it was from his side that Christ
fashioned the Church, as he had fashioned Eve from the side of Adam.
Moses gives a hint of this when he tells the story of the first man and
makes him exclaim: Bone from my bones and flesh from my flesh!
As God then took a rib from Adam’s side to fashion a woman, so Christ
has given us blood and water from his side to fashion the Church. God
took the rib when Adam was in a deep sleep, and in the same way Christ
gave us the blood and the water after his own death."
--- St. John Chrysostom, from The Catechesis