"Unless you eat the flesh of the Son of man and drink his blood"

(John 6:53-56 RSV) So Jesus said to them, "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; {54} he who eats my flesh and drinks my blood has eternal life, and I will raise him up at the last day. {55} For my flesh is food indeed, and my blood is drink indeed. {56} He who eats my flesh and drinks my blood abides in me, and I in him.
In the Aramaic language that Our Lord spoke, to symbolically "eat the flesh" or "drink the blood" of someone meant to persecute or assault them. See the following... (Psa 27:2 KJV) When the wicked, even mine enemies and my foes, came upon me to eat up my flesh, they stumbled and fell.
(Isa 9:18-20 RSV) For wickedness burns like a fire, it consumes briers and thorns; it kindles the thickets of the forest, and they roll upward in a column of smoke. {19} Through the wrath of the LORD of hosts the land is burned, and the people are like fuel for the fire; no man spares his brother. {20} They snatch on the right, but are still hungry, and they devour on the left, but are not satisfied; each devours his neighbor's flesh,
(Isa 49:26 RSV) I will make your oppressors eat their own flesh, and they shall be drunk with their own blood as with wine. Then all flesh shall know that I am the LORD your Savior, and your Redeemer, the Mighty One of Jacob."
(Micah 3:3 RSV) who eat the flesh of my people, and flay their skin from off them, and break their bones in pieces, and chop them up like meat in a kettle, like flesh in a caldron.
(2 Sam 23:17 RSV) "Far be it from me, O LORD, that I should do this. Shall I drink the blood of the men who went at the risk of their lives?" Therefore he would not drink it. These things did the three mighty men.
(Rev 17:6 RSV) And I saw the woman, drunk with the blood of the saints and the blood of the martyrs of Jesus. When I saw her I marveled greatly.
(Rev 17:16 NIV) The beast and the ten horns you saw will hate the prostitute. They will bring her to ruin and leave her naked; they will eat her flesh and burn her with fire.

Thus, if Jesus were only speaking symbolically about eating His flesh and drinking His blood, as the Protestants say, then what He really meant was "whoever persecutes and assaults me will have eternal life" -- which, of course, makes nonsense of the passage!

Bread and wine are not normal or natural symbols of flesh and blood. To call a man a "fox" is an understandable symbol for cleverness. To call a man "bread" is not an understandable symbol, without some explanation. Either the symbols would have been clearly explained (which is not the case) or Jesus spoke literally (which is the case!).

Taken from Beginning Apologetics, How to Explain and Defend the Catholic Faith, by San Juan Catholic Seminars, P.O. Box 5253, Farmington, NM 87499-52539889