from St. John Chrysostom’s catechumenate instruction (3.13-19) I’ve amended the text slightly for ease of reading.
If we wish to understand the power of Christ’s blood, we should go back to the ancient account of what took place in Egypt where Christ’s blood is foreshadowed. “Sacrifice a lamb without blemish,” Moses commanded, “and sprinkle its blood on your doors.”
Moses said, “Sacrifice a lamb without a blemish and smear the doors with its blood.” What does this mean? Can the blood of a sheep without reason save men endowed with reason? Yes, Moses replies, not because it is blood but because it is a sign of the Lord’s blood. So today if the devil sees, not the blood of the sign smeared on the doorposts, but the true blood smeared on the lips of the faithful, which are the doors of the temple of Christ, with all the more reason will he draw back.
If you desire further proof of the power of this blood, remember where it came from, how it ran down from the cross, flowing from the Master’s side. The gospel records that when Christ had died, but was still hanging on the cross, the soldier came and pierced his side with the spear and immediately there poured out water and blood. Now the water was a symbol of baptism and the blood, of the holy Eucharist. When that soldier pierced the Lord’s side, he breached the wall of the sacred temple, and I have found the treasure and made it my own. So also with the lamb: the Jews slaughtered the victim as a sacrifice and I gathered the fruit of that sacrifice—salvation. I have been saved by it.
“There flowed from his side water and blood.” Dearly beloved, do not pass over this mystery without reflection; 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: “by the washing of regeneration and the renewal of the Holy Spirit,” i.e., by baptism and by the holy Eucharist. Now the symbols of baptism and the Eucharist flowed from his side, it was from his side that Christ formed the Church, as he had formed 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.
Do you understand, then, how Christ has united his bride to himself? Have you seen with what kind of food he feeds us? By one and the same food we are both brought into being and fed. As a woman forms and feeds her child with her own blood and milk, so too does Christ continuously feed those whom he has begotten with his own blood— so too does Christ continuously feed those to whom he himself has given life.