As we see in John 6, many walked away. The Bible seems very clear, I know during the reformation the the three main leaders of the reformation each decided on their own definitions and who knows how many there are today.
Also in John 6, Jesus says:
60 When many of his disciples heard it, they said, “This is a hard saying; who can listen to it?” 61 But Jesus, knowing in himself that his disciples were grumbling about this, said to them, “Do you take offense at this? 62 Then what if you were to see the Son of Man ascending to where he was before? 63
It is the Spirit who gives life; the flesh is no help at all. The words that I have spoken to you are spirit and life. (emphasis added).
The Jews present were looking for another miracle from Jesus after the miracle of the loaves and fishes. They were thinking of their temporal needs (i.e. thinking with their stomachs). Jesus goes on to contrast the literal food (manna) they received in their wilderness journey, with the spiritual food He will supply them with through His death and resurrection. This is still long before the Last Supper. Since they were thinking in a literal sense he chose words that corresponded to their thinking. He makes a point that He who eats his "food" will never hunger again as He told the woman at the well that He who drinks the water he gives, shall never thirst again.
If you want to take that literally, then one participation in the Eucharist should suffice. You would not need to keep going back Sunday after Sunday. You would "never hunger again" or "never thirst again." Yet, you do keep going back. If the bread and wine literally became the body and blood of Christ, then as a human being His body had finite dimensions. We would have consumed all his body and all his blood thousands of years ago. In the multiplication of the loaves and fishes, God created new loaves and new fish so they could continue to eat. It was not the same loaf or the same few fish eaten over and over again.
As Jesus states in verse 63, it is the Spirit who gives life. The flesh is of no help at all. He is pointing out to them that while full bellies are satisfying, they do nothing for you spiritually. Jesus instructed the Apostles to "do this in remembrance of me" at the Last Supper. He instituted it as a memorial. We receive spiritual blessings from God through non-material means. If the Eucharist became Jesus' literal body and blood, then it would be through material means. The Bible tells us that Jesus' sacrifice on the cross was "once and for all." Yet the RCC re-sacrifices Him over and over again during the Mass. Once was not enough. The sacrifice was not "once and for all."
Justin Martyr (110–165) spoke of “the bread which our Christ gave us to offer
in remembrance of the Body which He assumed for the sake of those who believe in Him, for whom He also suffered, and also to the cup which He taught us to offer in the Eucharist,
in commemoration of His blood"(
Dialogue with Trypho, 70).
Clement of Alexandria explained that, “The Scripture, accordingly, has named wine
the symbol of the sacred blood” (
The Instructor, 2.2).
Origen similarly noted, “We have
a symbol of gratitude to God in the bread which we call the Eucharist” (
Against Celsus, 8.57).
Eusebius of Caesarea (263–340) espoused a symbolic view in his
Proof of the Gospel:
For with the wine which was indeed the symbol of His blood, He cleanses them that are baptized into His death, and believe on His blood, of their old sins, washing them away and purifying their old garments and vesture, so that they, ransomed by the precious blood of the divine spiritual grapes, and with the wine from this vine, "put off the old man with his deeds, and put on the new man which is renewed into knowledge in the image of Him that created him." . . . He gave to His disciples, when He said, "Take, drink; this is my blood that is shed for you for the remission of sins: this do in remembrance of me." And, "His teeth are white as milk," show the brightness and purity of the sacramental food. For again,
He gave Himself the symbols of His divine dispensation to His disciples, when He bade them make the likeness of His own Body. For since He no more was to take pleasure in bloody sacrifices, or those ordained by Moses in the slaughter of animals of various kinds, and was
to give them bread to use as the symbol of His Body, He taught the purity and brightness of such food by saying, “And his teeth are white as milk” (
Demonstratia Evangelica, 8.1.76–80).
Athanasius (296–373) similarly contended that the elements of the Eucharist are to be understood spiritually, not physically: “
[W]hat He says is not fleshly but spiritual. For how many would the body suffice for eating, that it should become the food for the whole world? But for this reason He made mention of the ascension of the Son of Man into heaven,
in order that He might draw them away from the bodily notion, and that from henceforth they might learn that
the aforesaid flesh was heavenly eating from above and spiritual food given by Him.” (
Festal Letter, 4.19)
Augustine (354–430), also, clarified that the Lord’s Table was to be understood in spiritual terms: “
Understand spiritually what I said; you are not to eat this body which you see; nor to drink that blood which they who will crucify me shall pour forth. . . . Although
it is needful that this be visibly celebrated, yet it must be spiritually understood” (
Exposition of the Psalms, 99.8).
He also explained the eucharistic elements as symbols. Speaking of Christ, Augustine noted: “He committed and delivered to His disciples
the figure [or symbol] of His Body and Blood.” (
Exposition of the Psalms, 3.1).
And in another place, quoting the Lord Jesus, Augustine further explained: “‘Except ye eat the flesh of the Son of man,’ says Christ, ‘and drink His blood, ye have no life in you.’ This seems to enjoin a crime or a vice;
it is therefore a figure [or symbol], enjoining that we should have a share in the sufferings of our Lord, and that we should retain a sweet and profitable memory of the fact that His flesh was wounded and crucified for us (
On Christian Doctrine, 3.16.24).
As you can see, not all the early church fathers held the view of
transubstantiation. They saw Christ's body and blood as figures and symbols to be spiritually understood. It is curious to me that the RCC quit serving wine at communion centuries ago suddenly insisting the priest was taking the wine for everyone and it was represented in the bread. Why withhold the wine if it is indeed the very blood of Christ? The RCC goes so far as to teach that the Lord is obligated to appear at Mass commanded to do so by the priest.
So far as I know, there are only two views of communion among Protestants.
Consubstantiation and the
Spiritual Presence view. Neither believes in the Catholic view of
transubstantiation.