The Jews did not believe Jesus that he said they had to eat his flesh an drink his blood. They walked away. If he was speaking metaphorically he would have called them back and said, “Hey guys, you don’t understand — see the Protestants have it right — what I just said is metaphor so you don’t have to be offended and walk away!” But he didn’t — he let the crowd of disciples walk away.
Your friend will also try to use this verse as an argument against you:
“It is the Spirit who gives life; the flesh profits nothing; the words that I have spoken to you are spirit and are life.” (John 6:63, NASB95)
He will probably say, “The flesh profits nothing, see!”
Concerning this, Jesus is not speaking about His Flesh (“My Flesh”), in verse 63 but “the flesh” which is very different and which is missed by sloppy-thinking Protestants like your friend. When Protestants claim “My flesh” profits nothing, they prove way too much! They are claiming that the Incarnation of Jesus in the flesh and the bodily resurrection has no profit.
What Jesus means by “”the flesh profits nothing” is very simple because he uses the phrase again in John 8:15 (we must let the Bible interpret the Bible
where he says:
“You judge according to the flesh; I judge no one.” (John 8:15, NKJV)
duccioultimacenaOther Bibles translate this “according to the flesh”, or “by human standards”, or “by appearances” or “with your human mind“. When Jesus uses the phrase “the flesh” he is referring to human understanding apart from divine revelation. Your friend judges the Eucharist by human standards (“Looks like bread, feels like bread, tastes like bread — must be bread”).
This statement of Jesus affirms what he has said about eating his Flesh and drinking his Blood and tells us it is a great mystery — spirit and life. With these words Jesus castigates the unbelieving Protestant along with the unbelieving Jews for judging spiritual things with earthly minds — by the flesh — and failing to understand the deep mysteries of God in the Eucharist.
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http://www.catholicconvert.com/blog/2009/05/12/the-eucharist-the-flesh-profits-nothing/