On the Holy Eucharist.

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.

A further note on Corpus Christi.

"The question whether soul and body are identical, therefore, is as superfluous as to ask whether wax and the shape imprinted on it are identical, or, in general whether the material of a thing is identical with the thing of which it is the material. "Is" and "one" have various meanings, but in their most legitimate meaning they connote the fully actual character of a thing."  Aristotle

Actually, this helps me to understand (or rather to clarify my own understanding of what happens at the Eucharist when the bread and wine are consecrated). Is the Sacrament the true Body of Chrisy? Answer: the bread and and wine AND the fleshly body TOGETHER are the actual body.  They are linked in the mystery that is sacrament and I go very Orthodox on that: 

"In the Eastern Orthodox Church, the Eucharistic celebration is known as the Divine Liturgy and is believed to impart the actual Body and Blood of Christ to the faithful. In the act of communion, the entire Church—past, present, and even future—is united in eternity. In Orthodox Eucharistic theology, although many separate Divine Liturgies may be celebrated, there is only one Bread and one Cup throughout all the world and throughout all time.

The most perfect expression of the Eucharistic unity of the church is found in the Hierarchical Divine Liturgy (a Liturgy at which a bishop is the chief celebrant), for as St. Ignatius of Antioch stated, where the bishop is, surrounded by his clergy and faithful, there is the church in all of her fullness.

The Anaphora (Eucharistic prayer) contains an anamnesis (lit. "making present") which not only recounts the historical facts of Jesus' death and resurrection, but actually makes them present, forming an undivided link to the unique event on Calvary. The Anaphora ends with an Epiclesis ("calling down from on high") during which the priest invokes the Holy Spirit to come and "change" the Gifts (elements of bread and wine) into the actual Body and Blood of Christ. Orthodox theology does not make use of the term "transubstantiation" to systematically describe how the Gifts become the Body and Blood of Christ; rather, they state that it is a Sacred Mystery, and prefer to use only the word "change". The Orthodox do not link the moment of transformation of the Gifts to the Words of Institution, or indeed to any one particular moment. They merely affirm that the change is completed at the Epiclesis."

And also: 

""Objective reality, but pious silence about technicalities" is the view of all the ancient Churches of the East, including the Eastern Orthodox, the Oriental Orthodox, the Eastern Catholic Churches) and the Assyrian Church of the East as well as perhaps most Anglicans and Lutherans. These, while agreeing with the Catholic belief that the sacrament is not merely bread and wine but truly the body and blood of Christ, and having historically employed the "substance" and "accidents" terminology to explain what is changed in the transformation, usually avoid this terminology, lest they seem to scrutinize the technicalities of the manner in which the transformation occurs."

This passage by the great Alexander Schmemann sums it up for me:

"For the Eucharist, we have said, is a passage, a procession leading the Church into "heaven," into her fulfillment as the Kingdom of God. And it is precisely the reality of this passage into the Eschaton that conditions the transformation of our offering — bread and wine — into the new food of the new creation, of our meal into the Messianic Banquet and the Koinonia of the Holy Spirit. Thus, for example, the coming together of Christians on the Lord’s Day, their visible unity "sealed" by the priest ("ecclesia in episcopo and episcopus in ecclesia") is indeed the beginning of the sacrament, the "gathering into the Church." And the entrance is not a symbolical representation of Christ going to preach but the real entrance — the beginning of the Church’s ascension to the Throne of God, made possible, inaugurated by the ascension of Christ’s Humanity. The offertory — the solemn transfer of bread and wine to the altar is again not the symbol of Christ’s burial (or of His entrance into Jerusalem) but a real sacrifice — the transfer of our lives and bodies and of the whole "matter" of the whole creation into heaven, their integration in the unique and all-embracing sacrifice of all sacrifices, that of Christ. The prosphora (offering) makes possible the anaphora — the lifting up of the Church, her eschatological fulfillment by the Eucharist. For Eucharist — "thanksgiving" — is indeed the very content of the redeemed life, the very reality of the Kingdom as "joy and peace in the Holy Spirit," the end and the fulfillment of our ascension into heaven. Therefore, the Eucharist is consecration and the Fathers called both the prayer of consecration and the consecrated gifts "Eucharist." The insistence by the Orthodox on the epiclesis is nothing else, in its ultimate meaning, but the affirmation that the consecration, i.e., the transformation of bread and wine into the Body and Blood of Christ, takes place in the "new eon" of the Holy Spirit. Our earthly food becomes the Body and Blood of Christ because it has been assumed, accepted, lifted up into the "age to come," where Christ is indeed the very life, the very food of all life and the Church is His Body, "the fullness of Him that filleth all in all" (Eph. 1:23). It is there, finally, that we partake of the food of immortality, are made participants of the Messianic Banquet, of the New Paschaleitourgia" which eternally transforms the Church into what she is, makes her the Body of Christ and the Temple of the Holy Spirit." (from "Theology and Eucharist", St. Vladimir’s Seminary Quarterly, Vol. 5, No. 4, Winter 1961, pp. 10-23