Nowhere else in the scripture is "eating flesh and drinking blood" used as some sort of metaphor or symbol of faith. The expression is used in a couple of places in the OT as a symbol of utter military defeat, as in "beaten so badly you'll resort to cannibalism". It's also a colloquial expression in some Semitic cultures for reviling someone.
When the Jews recoil in disgust from Jesus' teaching, he doesn't say "Hey, it's okay, I'm just talking about faith". No, he ratchets it up ... "for my flesh is true food, and my blood is true drink". Then, after the crowds leave, he doesn't corner the disciples and say, "You guys understand I'm just talking about faith, right?" No, he says, "Will you, too, go away?"
And it's not a coincidence that this whole episode happened at Passover, exactly a year before the Last Supper.
I guess Peter didn't get that message about having to eat the flesh and drink the blood, which btw would violate the prohibitions about doing so.
Did you read what those prohibitions actually say? Lev 17:11 ... "for the life of a creature is in the blood". Isn't that exactly the point? Don't you *want* to partake of the life of Jesus? Isn't that true life, as opposed to the death bequeathed to you by Adam? "I came that the world might have life, and have it abundantly ...", remember that?
If catholics really believe this then why not have real flesh and real blood at the service??
John 6:63
It is the spirit that quickeneth; the flesh profiteth nothing: the words that I speak unto you, they are spirit, and they are life.
Actually, He does.
John 6:59-69
Therefore many of His disciples, when they heard this said, “This is a difficult statement; who can listen to it?”
61But Jesus, conscious that His disciples grumbled at this, said to them, “Does this cause you to stumble?
62“What then if you see the Son of Man ascending to where He was before?
63“It is the Spirit who gives life; the flesh profits nothing; the words that I have spoken to you are spirit and are life.
64“But there are some of you who do not believe.” For Jesus knew from the beginning who they were who did not believe, and who it was that would betray Him.
65And He was saying, “For this reason I have said to you, that no one can come to Me unless it has been granted him from the Father.”
66As a result of this many of His disciples withdrew and were not walking with Him anymore.
67So Jesus said to the twelve, “You do not want to go away also, do you?”
68Simon Peter answered Him, “Lord, to whom shall we go? You have words of eternal life.
69“We have believed and have come to know that You are the Holy One of God.”
You see, it's always been about faith in Christ and always will be about faith in Christ. The message of faith and repentance is what was proclaimed by Christ, Paul, Peter and the whole NT.