You Gotta Eat The Lamb!
Jesus said I have come not to abolish the Law but fulfill it. His incarnate entry into our salvation history was not intended to abrogate all of Judaism prior to His advent and re-invent a completely disparate religion called "New Testament Christianity." To be sure, Jesus instituted a New Covenant through His blood, shed once and for all, for sin. But did establishing a New Covenant mean that all of Jewish history and God's dealings with His people needed to be cast aside? Through the "retrospectacles" of history we tend to view Christianity as this completely innovative movement which is the anti-thesis of Judaism. However, when we cut the Jewish roots from Christianity, we lose a perspective and historical way of thinking that was intended to inform our theology and help us understand our faith.
The doctrines of Catholicism have become easier for me to understand when I look to the Jewish roots of this religion. Note John the Baptist's first words regarding Jesus:
"Behold the Lamb of God who takes away the sins of the world."
This was such a vitally important statement to his Jewish followers because it distilled the concept of salvation from the past to the present and onto the future. His proclamation immediately connects all of Jewish history and the importance of the Passover to Jesus entry into our world. At the same time, John's announcement foreshadowed the Last Supper (and therefore the Mass) when Jesus gave us His body to eat.
Every Jew knew that to escape the angel of death they needed to "eat the lamb." It was a core belief of historical Judaism. The Passover was part of who they were as a people. It would follow then, that Jesus, when he commanded us to "take and eat for this is my body" was doing nothing less than continuing the pattern that God had instituted from the beginning of salvation history.
So I need to ask again, why is the sacrament of the Eucharist a human invention? Christ came not to abolish the law but to fulfill it. If you can accept the ancient Jewish paradigm that God required a spotless Lamb to be sacrificed for our sins, why not bring it to its logical completion? Bottom line: You Gotta Eat the Lamb!
ADDENDUM: This is what the Church historically has taught and practiced since 33 AD. The term "sacrifice of the altar" was used repeatedly by the early founders of Christianity to describe what transpired in the Mass. Just ask Emperor Diocletian why he slaughtered so many Christians in the early fourth century. He would tell you that the Christians were cannibals because they ate the flesh and drank the blood of the Son of Man.