Can you please tell me why we Catholics believe that the Eucharist is truly the body and blood of Christ, when practically no other Christians do?
Let me begin by saying that, in addition to Catholics, the Orthodox and Anglo-Catholics also believe in the Real Presence.
In view of the fact that Catholics alone, with 1.1 billion adherents, make up a majority of Christians, and that the Orthodox comprise several hundred million more, a great majority of all Christians in fact believe in the Real Presence.
But why do we believe that the Eucharist is not just a symbol but the Real Presence of Jesus? In simple terms, because it is abundantly clear in Scripture and Tradition, and the Church has always believed and taught it.
In the synagogue of Capernaum, Jesus spoke clearly of giving his flesh to eat and his blood to drink. “Truly, I tell you, unless you eat the flesh of the Son of Man and drink his blood, you have no life in you.
“Those who eat my flesh and drink my blood have eternal life, and I will raise them up on the last day; for my flesh is true food and my blood is true drink.” (Jn 6:53-55)
Jesus was speaking in very strong language. His listeners would have been horrified at the thought of eating someone’s flesh.
And as for drinking his blood, the Jews never ate meat with the blood still in it, because they regarded blood as the life principle of the animal and somehow sacred.
So even his disciples then said: “This teaching is difficult; who can accept it?” (Jn 6:60)
Many of his disciples left Jesus over his teaching on the Eucharist. (cf. Jn 6:66)
But Peter professed the faith of the Church in Jesus: “You have the words of eternal life. We have come to believe and know that you are the Holy One of God.” (Jn 6:68-69)
In other words, since Jesus was the very Son of God, the apostles could believe whatever he said, no matter how difficult it was to understand. This should be our attitude too.
Later, on instituting the Eucharist in the Last Supper, Jesus gave the apostles his flesh to eat and his blood to drink: “While they were eating, Jesus took a loaf of bread, and after blessing it he broke it, gave it to the disciples, and said, ‘Take, eat; this is my body.’ Then he took a cup, and after giving thanks he gave it to them, saying, ‘Drink from it, all of you; for this is my blood of the covenant, which is poured out for many for the forgiveness of sins.’” (Mt 26:26-28)
Jesus was not speaking of the bread and wine as mere symbols of his body and blood. He was truly giving them his body to eat and his blood to drink, under the appearances of bread and wine.
Some 20 years later, St Paul expressed the faith of the early Church in the Real Presence when he wrote to the Corinthians: “Whoever, therefore, eats the bread or drinks the cup of the Lord in an unworthy manner will be answerable for the body and blood of the Lord.” (1 Cor 11:27)
Right from the beginning, then, the Church believed that the Eucharist was truly the body and blood of Christ. There is a continuous tradition, beginning with the teaching of Jesus, passed on by the apostles in their preaching and writing, and accepted by the Church down the ages.
One of the earliest witnesses to this tradition is St Ignatius of Antioch, who died a martyr around 107 AD. He wrote: “The Eucharist is the flesh of our Saviour Jesus Christ; the flesh which suffered for our sins and which the Father, of his kindness, brought to life.” (Epist. ad Smyrn., 7, 1)
Half a century later, St Justin Martyr wrote: “For we do not receive this food as ordinary bread and as ordinary drink; but just as Jesus Christ our Saviour became flesh through the word of God, and assumed flesh and blood for our salvation, so too we are taught that the food over which the prayer of thanksgiving, the word received from Christ, has been said, the food which nourishes our flesh and blood by assimilation, is the flesh and blood of this Jesus who became flesh.” (Apol. 1, 66)
And for those who today regard the Eucharist as a mere symbol, Theodore of Mopsuestia wrote in the 5th century: “The Lord did not say: ‘This is the symbol of my body and this is the symbol of my blood.’ He said: ‘This is my body and my blood.’ He is teaching us not to pay attention to the nature of the object as presented to the senses.
“It has been changed into flesh and blood by the thanksgiving and the words pronounced over it.” (In Matt. Comm. 26)
The Fathers of the Church were unanimous in teaching the Real Presence.
So we can be absolutely certain we are interpreting Jesus’ words correctly when we believe in the Real Presence.