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." (John 6:52-58)
THE BLESSED SACRAMENT THE TOUCH-STONE OF FAITH: He who does not believe in the Real Presence of our Lord in the Holy Eucharist, has no part in Him, because he has no firm belief in the Divinity of Christ. The true believer does not ask, as did the Jews: "How can this be?" but believes the words of Christ unconditionally, because he knows that Christ is the Son of God, and that with God all things are possible.
[From 'A Practical Commentary on Holy Scripture' by Bishop Knecht, D.D.]
(1899 Douay-Rheims Bible)