Steadfast, check this out also. It contains patristic comments on St.John 6 which Roman Catholics and Eastern Orthodox often quote in support of their views. It is obvious to me that the understanding of the early church was pretty different compared to the current position of RCC and EOC .
"If the sentence is one of command, either forbidding a crime or vice, or enjoining an act of prudence or benevolence, it is not figurative. If, however, it seems to enjoin a crime or vice, or to forbid an act of prudence or benevolence, it is figurative. 'Except ye eat the flesh of the Son of man,' says Christ, 'and drink His blood, ye have no life in you.' This seems to enjoin a crime or a vice; it is therefore a figure, enjoining that we should have a share in the sufferings of our Lord, and that we should retain a sweet and profitable memory of the fact that His flesh was wounded and crucified for us." - Augustine (On Christian Doctrine, 3:16:24)
"Elsewhere the Lord, in the Gospel according to John, brought this out by symbols, when He said: 'Eat ye my flesh, and drink my blood,' describing distinctly by metaphor the drinkable properties of faith and the promise, by means of which the Church, like a human being consisting of many members, is refreshed and grows, is welded together and compacted of both,--of faith, which is the body, and of hope, which is the soul; as also the Lord of flesh and blood. For in reality the blood of faith is hope, in which faith is held as by a vital principle." - Clement of Alexandria (The Instructor, 1:6)
"He says, it is true, that 'the flesh profiteth nothing;' but then, as in the former case, the meaning must be regulated by the subject which is spoken of. Now, because they thought His discourse was harsh and intolerable, supposing that He had really and literally enjoined on them to eat his flesh, He, with the view of ordering the state of salvation as a spiritual thing, set out with the principle, 'It is the spirit that quickeneth;' and then added, 'The flesh profiteth nothing,'--meaning, of course, to the giving of life. He also goes on to explain what He would have us to understand by spirit: 'The words that I speak unto you, they are spirit, and they are life.' In a like sense He had previously said: 'He that heareth my words, and believeth on Him that sent me, hath everlasting life, and shall not come into condemnation, but shall pass from death unto life.' Constituting, therefore, His word as the life-giving principle, because that word is spirit and life, He likewise called His flesh by the same appellation; because, too, the Word had become flesh, we ought therefore to desire Him in order that we may have life, and to devour Him with the ear, and to ruminate on Him with the understanding, and to digest Him by faith. Now, just before the passage in hand, He had declared His flesh to be 'the bread which cometh down from heaven,' impressing on His hearers constantly under the figure of necessary food the memory of their forefathers, who had preferred the bread and flesh of Egypt to their divine calling." - Tertullian (On the Resurrection of the Flesh, 37)
"'He that eateth me,' He says, 'he also shall live because of me;' for we eat His flesh, and drink His blood, being made through His incarnation and His visible life partakers of His Word and of His Wisdom. For all His mystic sojourn among us He called flesh and blood, and set forth the teaching consisting of practical science, of physics, and of theology, whereby our soul is nourished and is meanwhile trained for the contemplation of actual realities. This is perhaps the intended meaning of what He says." - Basil (Letter 8:4)
"You know that in ordinary parlance we often say, when Easter is approaching, 'Tomorrow or the day after is the Lord's Passion,' although He suffered so many years ago, and His passion was endured once for all time. In like manner, on Easter Sunday, we say, 'This day the Lord rose from the dead,' although so many years have passed since His resurrection. But no one is so foolish as to accuse us of falsehood when we use these phrases, for this reason, that we give such names to these days on the ground of a likeness between them and the days on which the events referred to actually transpired, the day being called the day of that event, although it is not the very day on which the event took place, but one corresponding to it by the revolution of the same time of the year, and the event itself being said to take place on that day, because, although it really took place long before, it is on that day sacramentally celebrated. Was not Christ once for all offered up in His own person as a sacrifice? and yet, is He not likewise offered up in the sacrament as a sacrifice, not only in the special solemnities of Easter, but also daily among our congregations; so that the man who, being questioned, answers that He is offered as a sacrifice in that ordinance, declares what is strictly true? For if sacraments had not some points of real resemblance to the things of which they are the sacraments, they would not be sacraments at all. In most cases, moreover, they do in virtue of this likeness bear the names of the realities which they resemble. As, therefore, in a certain manner the sacrament of Christ's body is Christ's body, and the sacrament of Christ's blood is Christ's blood,' in the same manner the sacrament of faith is faith." (Letter 98:9)
"But He instructed them, and saith unto them, 'It is the Spirit that quickeneth, but the flesh profiteth nothing; the words that I have spoken unto you, they are spirit, and they are life.' Understand spiritually what I have said; ye are not to eat this body which ye see; nor to drink that blood which they who will crucify Me shall pour forth."-Augustine (Expositions on the Psalms, 99:8)
"It may be also understood in this way: 'The poor ye will have always with you, but me ye will not have always.' The good may take it also as addressed to themselves, but not so as to be any source of anxiety; for He was speaking of His bodily presence. For in respect of His majesty, His providence, His ineffable and invisible grace, His own words are fulfilled, 'Lo, I am with you alway, even to the end of the world.' But in respect of the flesh He assumed as the Word, in respect of that which He was as the son of the Virgin, of that wherein He was seized by the Jews, nailed to the tree, let down from the cross, enveloped in a shroud, laid in the sepulchre, and manifested in His resurrection, 'ye will not have Him always.' And why? Because in respect of His bodily presence He associated for forty days with His disciples, and then, having brought them forth for the purpose of beholding and not of following Him, He ascended into heaven and is no longer here. He is there, indeed, sitting at the right hand of the Father; and He is here also, having never withdrawn the presence of His glory. In other words, in respect of His divine presence we always have Christ; in respect of His presence in the flesh it was rightly said to the disciples, 'Me ye will not have always.' In this respect the Church enjoyed His presence only for a few days: now it possesses Him by faith, without seeing Him with the eyes."-Augustine (Lectures on the Gospel of John, 50:13)
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Not all fathers were in consensus about the Eucharist though. Already with St.John Chrysostom we can find that he truly considers Eucharist as a true propitiatory sacrifice to be offered even for the dead to appease God. And as time passed by and as spirituality decreased and mysticism and ritualism prevailed you can find more and more leaning towards RCC and EOC position.
Anyway, the fact is that the Church in the first 400 years was decisively (in large majority) in the favour of Anglican/Reformed view of the Eucharist.
