St. John Damascene: The Body and Blood of Christ

"WHEREFORE to those who partake worthily with faith, it is for the remission of sins and for life everlasting and for the safeguarding of soul and body; but to those who partake unworthily without faith, it is for chastisement and punishment, just as also the death of the Lord became to those who believe life and incorruption for the enjoyment of eternal blessedness, while to those who do not believe and to the murderers of the Lord it is for everlasting chastisement and punishment.

"The bread and the wine are not merely figures of the body and blood of Christ (God forbid!) but the deified body of the Lord itself: for the Lord has said, “This is My body,” not, this is a figure of My body: and “My blood,” not, a figure of My blood. And on a previous occasion He had said to the Jews, "Except you eat the flesh of the Son of Man and drink His blood, you have no life in you. For My flesh is meat indeed and My blood is drink indeed. And again, He that eats Me, shall live (Jn 6:51-55)." "

~St. John Damascene: Exposition of the Orthodox Faith, Bk IV, Chap. 13.

The Institution of the Eucharist, by Joos van Wassenhove.
Oil on wood, 1473-75; Galleria Nazionale delle Marche, Urbino.