In the following I respond.
I fail to see how one can take it as symbolic considering the reaction of his disciples in John 6.
Jesus comment was that he was the fulfillment of the Old Testament manna:
31Our fathers did eat manna in the desert; as it is written, He gave them bread from heaven to eat. 32Then Jesus said unto them, Verily, verily, I say unto you, Moses gave you not that bread from heaven; but my Father giveth you the true bread from heaven. 33For the bread of God is he which cometh down from heaven, and giveth life unto the world.
That the manna was a symbol of Christ is beyond reasonable question.
The main initial objection by the Jews was: "you're not from heaven, you're from your father, Joseph, and your mother, Mary."
41The Jews then murmured at him, because he said, I am the bread which came down from heaven. 42And they said, Is not this Jesus, the son of Joseph, whose father and mother we know? how is it then that he saith, I came down from heaven?
Jesus' response was to say that if they knew His Father, they would know Him.
But Jesus continued to repeat His claim to be the fulfillment of the manna:
47Verily, verily, I say unto you, He that believeth on me hath everlasting life. 48I am that bread of life. 49Your fathers did eat manna in the wilderness, and are dead. 50This is the bread which cometh down from heaven, that a man may eat thereof, and not die. 51I am the living bread which came down from heaven: if any man eat of this bread, he shall live for ever: and the bread that I will give is my flesh, which I will give for the life of the world.
Jesus' point is that he gives life through faith. The fathers ate manna and died, but if someone eats Jesus' flesh and blood they will live and not die.
Now, very few Christians - if any - would be so vain in their imagination as to think that Jesus was saying that the life that he gives is physical life. Instead, it is spiritual life - eternal life. Jesus is the spiritual fulfillment of the physical Old Testament symbol.
If we take "life" spiritually we ought also to take the consumption of his body and blood spiritually. It is by faith in Him that we are nourished by Him.
But the disciples were again confused, and did not recognize the the spiritual sense of Jesus' words.
So Jesus again compared his work to that of the physical manna:
52The Jews therefore strove among themselves, saying, How can this man give us his flesh to eat? 53Then Jesus said unto them, Verily, verily, I say unto you, Except ye eat the flesh of the Son of man, and drink his blood, ye have no life in you. 54Whoso eateth my flesh, and drinketh my blood, hath eternal life; and I will raise him up at the last day. 55For my flesh is meat indeed, and my blood is drink indeed. 56He that eateth my flesh, and drinketh my blood, dwelleth in me, and I in him. 57As the living Father hath sent me, and I live by the Father: so he that eateth me, even he shall live by me. 58This is that bread which came down from heaven: not as your fathers did eat manna, and are dead: he that eateth of this bread shall live for ever.
Jesus even explains (in verse 57) that the way in which we "eat" him is the same way in which He lives by the Father. All who realize that His Father is not Joseph, should realize that Father does not have a body. The way that the Father nourishes Jesus is through spiritual union. Even so, we are nourished through spiritual union with (by faith in) Jesus Christ.
Those who are nourished by spiritual union with Christ will have spiritual and eternal life. They will still physically die. We should recognize that Christ is not speaking of literal, physical life.
Nevertheless, some of His disciples were offended by what Jesus said, for we read:
60Many therefore of his disciples, when they had heard this, said, This is an hard saying; who can hear it? 61When Jesus knew in himself that his disciples murmured at it, he said unto them, Doth this offend you? 62What and if ye shall see the Son of man ascend up where he was before? 63It is the spirit that quickeneth; the flesh profiteth nothing: the words that I speak unto you, they are spirit, and they are life. 64But there are some of you that believe not. For Jesus knew from the beginning who they were that believed not, and who should betray him. 65And he said, Therefore said I unto you, that no man can come unto me, except it were given unto him of my Father. 66From that time many of his disciples went back, and walked no more with him.
Notice that Jesus addresses the main source of their offense first: his deity. Jesus asks them whether they will believe if they see Him ascend to the place from whence He descended. In other words, Jesus identifies that objection (the first one the Jews raised) as the primary objection and did not back down from it.
As for the issues regarding His flesh comments, Jesus also clarified, in verse 63, that He is comparing spiritual nourishment (the nourishment he provides) with fleshly nourishment (manna), and says that the fleshly profits nothing.
Indeed, Jesus points them back to the words that He speaks (the words we now have recorded in Scripture) and says that they are spirit and life.
Nevertheless, Jesus points out there were some of the disciples who did not believe His words - as noted above, they were offended by His claim of divinity. Jesus explains that the reason they do not all believe is because God the Father did not give all of them to Him. This failure to recant His claim turned away many disciples.
They were literally aghast at the implication.
They were primarily aghast at the claim of divinity. They mocked with a literal interpretation his claim to provide his flesh and blood.
IN fact, many of them left him over the claims they'd have to eat His flesh and drink His blood.
As noted above, they left because He claimed to be God and claimed they didn't believe Him because they didn't know His Father and His Father did not give them to Him. They were offended and left.
Note also how they disputed among themselves saying "How can this man give us his flesh to eat?"
Notice how "the Jews" were the ones who made that inquiry, as distinguished from His disciples. Notice how verse 59 divides the account into the public comments of Jesus (before verse 59) and the private comments of Jesus (after verse 59).
But Our Lord, rather than explaining it as figurative, like He did when they didn't understand some other teachings of His, instead re-emphasizes things! "Truly, truly, I say to you, unless you eat the flesh of the Son of man and drink his blood, you have no life in you; he who eats my flesh and drinks my blood has eternal life, and I will raise him up at the last day. For my flesh is food indeed, and my blood is drink indeed. He who eats my flesh and drinks my blood abides in me, and I in him"
Actually, as noted above, Jesus did emphasize the spirituality of His nourishment, both in his private discourse to the disciples and by comparing it the nourishment He receives from His Father.
If you look at this in aramaic, you'll find the language here is quite carnal and forceful, as if He was deliberately emphasizing the literalness of His statements.
A) Of course, John was written in Greek, not Aramaic. The Peshitta is a translation of the Greek original. That said, the idea that the language is "carnal and forceful" is contradicted by verse 63, which says that the words He speaks are spirit.
B) I have no doubt that this "carnal and forceful" is the spin placed on this text by some (probably contemporary) Roman Catholic (or possibly Eastern Orthodox) commentator. The reason for that view of the text is clear (without getting entangled in arguments over the "tone" of an ancient language): the author is seeking to support by tone what cannot be supported by exegesis.
He then warns them not to think with just their human minds, but to open it up to the Holy Spirit to give them understanding and help them believe when He says, "It is the Spirit that gives life, the flesh is of no avail; the words that I have spoken to you are spirit and life"
No, that is not a warning not to think with their human minds (or "just their human minds"). It is distinguishing a fleshly, literal interpretation of his description of his nourishment from a spiritual and correct interpretation of his nourishing provision for His people.
The plain reading of the scripture seems to leave the burden of proof on those who insist it to be symbolic.
Actually, the plain reading of the Scripture is that Christ was speaking of spiritual nourishment, not physical nourishment.Indeed, this is confirmed by Peter's explanation as to WHY he and the other disciples (in general, Judas had other reasons) stayed:
68Then Simon Peter answered him, Lord, to whom shall we go? thou hast the words of eternal life. 69And we believe and are sure that thou art that Christ, the Son of the living God.
Peter confessed that they believed the words of Christ and His claim to deity.
The reaction of the crowd, Jesus re-emphasizing the literalness instead of explaining it as otherwise, His warnings that it cannot be understood without the Spirit, and the fact that many disciples left after this seem to be quite clear that He said something that made no sense to them. "How can this man give us his flesh to eat?"
No, it is not just that it cannot be understood without the spirit: it is that the nourishment that Christ gives is better than manna for it is spiritual nourishment, not fleshly nourishment. It gives spiritual life that never dies - whereas manna gave only mortal life for a season.
How? Because He is Lord. If Jesus wanted to, He can make stones into bread. How can I doubt Him when He says that the bread IS His body?
And - of course - the response is that we are not to doubt Him, but rather to understand Him. We are not to impose a foolish physical interpretation on His words, like that unbelieving Jews, but to understand that the Lord's Supper, like manna, is a physical symbol of Christ.It is the one proper icon of Christ.
May our Manna be praised!