A very interesting passage that friend showed me sometime ago from St. Theodoret of Cyprus, from Eranistes, Dialog 2. Note that the Orthodox responder in this dialog confesses that the substance of bread and wine remain in the Eucharist, even as we confess that they become Christ's true body and blood:
Eran.--You have opportunely introduced the subject of the divine mysteries for from it I shall be able to show you the change of the Lord's body into another nature. Answer now to my questions.
Orth.--I will answer.
Eran.--What do you call the gift which is offered before the priestly invocation?
Orth.--It were wrong to say openly; perhaps some uninitiated are present.
Eran.--Let your answer be put enigmatically.
Orth.--Food of grain of such a sort.
Eran.--And how name we the other symbol?
Orth.--This name too is common, signifying species of drink.
Eran.--And after the consecration how do you name these?
Orth.--Christ's body and Christ's blood.
Eran.--And do you believe that you partake of Christ's body and blood?
Eran.--As, then, the symbols of the Lord's body and blood are one thing before the priestly invocation, and after the invocation are changed and become another thing; so the Lord's body after the assumption is changed into the divine substance.
Orth.--You are caught in the net you have woven yourself. *For even after the consecration the mystic symbols are not deprived of their own nature; they remain in their former substance figure and form*; they are visible and tangible as they were before. But they are regarded as what they are become, and believed so to be, and are worshipped as being what they are believed to be. Compare then the image with the archetype, and you will see the likeness, for the type must be like the reality. For that body preserves its former form, figure, and limitation and in a word the substance of the body; but after the resurrection it has become immortal and superior to corruption; it has become worthy of a seat on the right hand; it is adored by every creature as being called the natural body of the Lord.
Eran.--Yes; and the mystic symbol changes its former appellation; it is no longer called by the name it went by before, but is styled body. So must the reality be called God, and not body.
Orth.--You seem to me to be ignorant--for He is called not only body but even bread of life. So the Lord Himself used this name' and that very body we call divine body, and giver of life, and of the Master and of the Lord, teaching that it is not common to every man but belongs to our Lord Jesus Christ Who is God and Man. "For Jesus Christ" is "the same yesterday, to-day, and forever."