Is it possible that the warning is for you and your ilk?
You give me a warning. I give you a promise from Christ:
He that eateth my flesh, and drinketh my blood, dwelleth in me, and I in him.
You want to take what He said to the Jews in sarcasm because they were still NOT believing Him in how to receive the bread of life which was by believing in Him? Jesus was not talking about communion at all in that chapter but about how they can be saved. See proof that the Jews were not believing Him on how to receive that bread of life.
John 6:32 Then 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. 33 For the bread of God is he which cometh down from heaven, and giveth life unto the world. 34 Then said they unto him, Lord, evermore give us this bread.
35 And Jesus said unto them, I am the bread of life: he that cometh to me shall never hunger; and he that believeth on me shall never thirst. 36 But I said unto you, That ye also have seen me, and believe not.
They had asked Him to give them that bread in verse 34 and Jesus told them how to receive that bread... by believing in Him, and Jesus pointed out afterwards that they were not believing Him when He had said that. That led to Him being sarcastic to the unbelieving Jews that you are quoting.
Jesus spoke the truth again to His disciples that by believing in Him is how one receives the bread of
life as in eternal life.
John 6:61 When Jesus knew in himself that his disciples murmured at it, he said unto them, Doth this offend you? 62 What and if ye shall see the Son of man ascend up where he was before?
( that's talking about His ascension after His resurrection ) 63 It is the spirit that quickeneth;
the flesh profiteth nothing: ( that means the eating of the bread profits nothing ) the words that I speak unto you, they are spirit, and they are life. 64 But there are some of you that believe not.
( Once again, Jesus points out how not believing in Him is how they are not receiving the bread of life ) For Jesus knew from the beginning who they were that believed not, and who should betray him.
So you decide if you want to continue in the RCC's error for picking verses out that was done in sarcasm to the unbelieving Jews or take what Jesus said to His believing disciples on how to receive that bread of life as in eternal life... by believing in Him.
If you take verse 35 as meaning communion....
John 6:
35 And Jesus said unto them, I am the bread of life: he that cometh to me shall never hunger; and he that believeth on me shall never thirst.
Then the RCC and you would only take communion once, otherwise you would make Jesus look like a liar when you take it again when He had promised that you would never hunger nor thirst for that again.
But He was talking about receiving Him at your salvation as Him being in you always is proof that you are saved and have eternal life.
It's not like the unbelieving Jews turned on Him and began eating Him for how the RCC is taking His words of sarcasm to the unbelieving Jews. Neither did His disciples and they, except for Judas Iscariot, believed His words and thus believed Him to be the Christ, the Son of the living God.
And a warning from Paul: Wherefore whosoever shall eat this bread, and drink this cup of the Lord, unworthily, shall be guilty of the body and blood of the Lord.
Mary
I submit to you that taking communion for any other reason other than what He said to take it for which was to be done in remembrance of Him is taking the bread & cup of the Lord in an unworthy manner.
It was before His crucifixion when Jesus had broken bread and sup the cup with His disciples; not afterwards.