On the subject of the Christian understanding of the Eucharist, one of the earliest references to it lies in the First Apology of St Justin Martyr He wrote the following passage around about 155 AD:
"And this food is called among us Εὐχαριστία [the Eucharist] ... For not as common bread and common drink do we receive these; but in like manner as Jesus Christ our Saviour, having been made flesh by the Word of God, had both flesh and blood for our salvation, so likewise have we been taught that the food which is blessed by the prayer of His word, and from which our blood and flesh by transmutation are nourished, is the flesh and blood of that Jesus who was made flesh."
However, just to make life ambiguous (we're talking theology here - that's what it does) he also wrote in his Dialogue with Trypho, ch 70: "Now it is evident, that in this prophecy to the bread which our Christ gave us to eat, in remembrance of His being made flesh for the sake of His believers, for whom also He suffered; and to the cup which He gave us to drink, in remembrance of His own blood, with giving of thanks." From which it is entirely possible to derive a much more Reformed understanding of the Eucharist. Read literally, Justin was both a Zwinglian and a Transubstantion support. Which is both very unlikely and somewhat schizophrenic.
Ultimately all these theories about what happens at the Eucharist are just that. Theories. Informed pious speculation, often combined with a sort of intellectual mission to put theology in terms acceptable and coherent with the fashionable philosphy of the day. To most of us that's pretty irrelevant. Our concern is much more personal and practical. What does this mean to me and what does it do for my spiritual life?
Cardinal Newman put it nicely:
- I place myself in the presence of Him,
in whose Incarnate Presence I am before.
- I place myself there.
- I adore You, O my Saviour, present here as God and Man,
in Soul and Body, in true Flesh and Blood.
- I acknowledge and confess that I kneel before the Sacred Humanity,
- which was conceived in Mary’s womb, and lay in Mary’s bosom;
- which grew up to man’s estate, and by the Sea of Galilee called the Twelve, wrought miracles, and spoke words of wisdom and peace;
which in due season hung on the cross,
- lay in the tomb, rose from the dead, and now reigns in heaven.
- I praise and bless, and give myself wholly to Him,
- Who is the true Bread of my soul, and my everlasting joy.