In the Catholic faith, we believe that when the priest prays the words of consecration, the host and wine are transubstantiated into the true Body and Blood of Christ, under the form of bread and wine. We get this from the Last Supper, and from John 6, I’m not sure of the exact verses since my bible app does not have the numbers of he verses.
“I am the living bread which came down from heaven.
If any man eat of this bread, he shall live for ever: and the bread that I will give is my flesh, for the life of the world.
The Jews therefore strove among themselves, saying: How can this man give us his flesh to eat?
Then Jesus said to them: Amen, amen, I say unto you: except you eat the flesh of the Son of man and drink his blood, you shall not have life in you.
He that eateth my flesh and drinketh my blood hath everlasting life: and I will raise him up in the last day.
For my flesh is meat indeed: and my blood is drink indeed.
He that eateth my flesh and drinketh my blood abideth in me: and I in him.
As the living Father hath sent me and I live by the Father: so he that eateth me, the same also shall live by me.
This is the bread that came down from heaven. Not as your fathers did eat manna and are dead. He that eateth this bread shall live for ever.
These things he said, teaching in the synagogue, in Capharnaum.
Many therefore of his disciples, hearing it, said: This saying is hard; and who can hear it?
But Jesus, knowing in himself that his disciples murmured at this, said to them: Doth this scandalize you?
If then you shall see the Son of man ascend up where he was before?
It is the spirit that quickeneth: the flesh profiteth nothing. The words that I have spoken to you are spirit and life.
But there are some of you that believe not. For Jesus knew from the beginning who they were that did not believe and who he was that would betray him.
And he said: Therefore did I say to you that no man can come to me, unless it be given him by my Father.
After this, many of his disciples went back and walked no more with him.”
The parts in bold are there for emphasis; Jesus said his flesh was true meat and his blood true drink. Christ was very figurative in his preaching, and had to explain many of his parables. But, when his disciples began to leave, he did not say, “wait kidding I was just using figurative language here let me explain.” He let them go, because he understood that they would find this concept very weird, and not pleasant.
The reason why non-Catholics cannnot receive the Eucharist is because you must believe that it is the Body, Blood, Soul and Divinity of Christ contained in the Host, which is the wafer of bread after it has been consecrated. The Precious Blood is the wine, and is also the body blood soul and divinity of Christ. If you do not truly believe this, than the you could not have the proper reverance and humility due Him when receiving communion. To be Catholic is to say you believe this.
