Catholics believe in the Real Presence of Jesus in the Eucharist, meaning that what appears to be bread and wine is really Jesus’ body and blood—not just a symbol of his body and blood. When Catholics receive Holy Communion, it is an expression of the unity among all those in communion with the Catholic Church throughout the world, who maintain the belief in the Real Eucharistic Presence of Christ. Therefore, only those who believe in the True Presence may participate in this sacrament of oneness with Christ and his Church. “… [T]he celebration of the Eucharistic sacrifice is wholly directed toward the intimate union of the faithful with Christ through communion” (CCC 1382). 
 
Ultimately, Catholics believe that we cannot celebrate this unifying sacrament with other Christians while there are disagreements about the Eucharist itself. However, Catholics pray for the day when we can reconcile with other Christians and share in the unity of God’s people through the Holy Eucharist. 
 
The United States Conference of Catholic Bishops expresses this desire for unity: 
 
“We pray that our common baptism and the action of the Holy Spirit in this Eucharist will draw us closer to one another and begin to dispel the sad divisions which separate us. We pray that these will lessen and finally disappear, in keeping with Christ’s prayer for us ‘that they may all be one’” (John 17:21).

The Catholic doctrine of the Real Presence is the belief that Jesus Christ is literally, not symbolically, present in the Holy Eucharist—body, blood, soul and divinity. Catholics believe in the Real Presence of Christ in the Eucharist because Jesus tells us this is true in the Bible: “I am the bread of life. Your fathers ate the manna in the wilderness, and they died. This is the bread which comes down from heaven, that a man may eat of it and not die. I am the living bread which came down from heaven; if any one eats of this bread, he will live for ever; and the bread which I shall give for the life of the world is my flesh. The Jews then disputed among themselves, saying, ‘How can this man give us his flesh to eat?’ 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; 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” (John 6:48-56). Furthermore, the early Church Fathers either imply or directly state that the bread and wine offered in the celebration of the Lord’s Supper is really the body and blood of Jesus Christ. In other words, the doctrine of the Real Presence that Catholics believe today was believed by the earliest Christians 2,000 years ago. 
 
This miracle of God’s physical presence to us at every Mass is the truest testament to Christ’s love for us and His desire for each of us to have a personal relationship with Him. 
 
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).