“The bread and the wine are not merely figures of the body and blood of Christ (God forbid!) but the deified body of the Lord itself: for the Lord has said, "This is My body", not, "this is a figure of My body": and "My blood", not, "a figure of My blood". And on a previous occasion He had said to the Jews, "Unless you eat the flesh of the Son of Man and drink His blood, you have no life in you. For My flesh is meat indeed and My blood is drink indeed." And again, "He that eats Me, shall live" (John 6:51-55).“
— St. John Damascene,
Exposition of the Orthodox Faith, Bk. 4 Chap. 13
Martin Luther famously wrote that the doctrine of Sola Fide ("Faith Alone") was the "doctrine upon which the Church stands or falls." While Luther was correct about the centrality of faith for the Christian, the question then becomes: "faith in what?" For him, the answer was “the Word of God,” and rightly so.
Christian worship for the first 1500 years was centered around the Eucharist ("gift"), but it wasn't anything like the "communion" that many Protestant churches offer now. Rather than merely some memorial service, the Church has always taught that the Eucharist is truly Christ's Body and Blood, by which we live and without which we can't. Jesus doesn't mince words in John 6, and to deny that He meant what He said comes dangerously close to having faith in our own understanding rather than in the words of Christ Himself.
Within Protestantism, the Pentecostal movement of the last century complained of a lack of miracles in the church...well, here is the true miracle! And it is a miracle that has happened weekly—even daily!—around the world ever since the earliest days of the Church. The eternal invitation to the Lord's table is an invitation to the altar upon which He has given Himself up for us for the forgiveness of sin. We do it in remembrance of Him, but also in remembrance of His words, which communicate to us something so baffling that it must either be absolutely true, or else the ravings of a madman.
To paraphrase Joshua 24:15, “choose this day whom ye will believe”; whether we believe Christ’s words or lean on our own understanding, the option is left to us as to where to place our faith.