Devin Rose wrote (in part):
We were discussing the Eucharist: they both believe in the symbolic-only Eucharist (ala Zwingli and the Baptists) whereas I as a Catholic believe in transubstantiation. I asked them how can we know what the Apostles believed on this subject, given that we disagree with each other on how to interpret the Bible on this doctrine.(source)
They said it comes down to their belief in the Bible and how clearly it teaches the symbolic-only Eucharist. I told them that, since we disagree on the interpretation, what if we looked at other sources, say, two of the early Christian leaders whose writings we know are authentic: St. Ignatius of Antioch and St. Justin Martyr. I am sure you are familiar with what they wrote about the Eucharist. In short, they unequivocally speak of the bread and the wine becoming the body and blood of Christ. Even if one were to try to interpret their words in the most Baptist-leaning way possible, they fall much closer to the Catholic (and Lutheran and even Calvinist) belief on the Eucharist than the Zwinglian/Baptist symbolic belief.
I have four main responses:
1) Yes, your friends are right to go to the Scriptures. Since Scripture dates to the time of the apostles, is inspired, and (in many cases) was penned by an apostle, it is the best possible evidence as to what the Apostles believed. Going to an apostolic father (like Ignatius) or to a very early Christian writer (like Justin Martyr) is only second and third best (Ignatius was in an overlapping generation with the apostles and Justin Martyr was in one of the first generations that did not overlap with the apostles). Similarly, while we know the text of Scripture with high confidence for virtually all its verses, the text of Ignatius is actually open to significant doubt at many places. Not only are many of the letters attributed to him inauthentic, but the authentic letters have been variously interpolated over the years so that we have, in essence, two versions - a long version in which we have little confidence that it is fully authentic - and a short version in which we have higher confidence that it is authentic. The text of Justin Martyr is substantially less controversial, but again - the textual transmission of Justin Martyr is nowhere near as good as the textual transmission of the Scriptures, especially the New Testament.
2) In point of fact, the Scriptures are sufficient to resolve the matter as to what the Apostles believed. But if you will insist that the Scriptures are ambiguous or somehow lack sufficient authority, we can examine with you the historical record of tradition. Nevertheless, the historical record shows that the Roman Catholic doctrine of transubstantiation is something developed rather late. The term itself doesn't come around for about a thousand years or so. The concept without the word is also not found. In other words, we don't find the accidents/substance distinction being enunciated by the fathers of the church significantly prior to the development of the term.
3) As to the specific instances of Ignatius and Justin Martyr, they do use expressions that are frequently used in this sort of discussion. The two most popular quotations alleged from Ignatius are the following (taken from an article on the Real Presence at Catholic.com - link to the article):
"I have no taste for corruptible food nor for the pleasures of this life. I desire the bread of God, which is the flesh of Jesus Christ, who was of the seed of David; and for drink I desire his blood, which is love incorruptible" (Letter to the Romans 7:3 [A.D. 110]).
(I've previously demonstrated that this quotation doesn't teach transubstantiation.)
"Take note of those who hold heterodox opinions on the grace of Jesus Christ which has come to us, and see how contrary their opinions are to the mind of God. . . . They abstain from the Eucharist and from prayer because they do not confess that the Eucharist is the flesh of our Savior Jesus Christ, flesh which suffered for our sins and which that Father, in his goodness, raised up again. They who deny the gift of God are perishing in their disputes" (Letter to the Smyrnaeans 6:2–7:1 [A.D. 110]).
(Similarly, I've also previously demonstrated that this quotation doesn't teach transubstantiation.)
As noted above, I've previously demonstrated that these quotations don't teach transubstantiation. However, I could have gone further. Note that Ignatius uses words that sound like a literal identification between the bread and the flesh. But consider that Ignatius elsewhere makes a similar identification:
Not that I know there is anything of this kind among you; but I put you on your guard, inasmuch as I love you greatly, and foresee the snares of the devil. Wherefore, clothing yourselves with meekness, be renewed in faith, that is the flesh of the Lord, and in love, that is the blood of Jesus Christ. Let no one of you cherish any grudge against his neighbour. Give no occasion to the Gentiles, lest by means of a few foolish men the whole multitude [of those that believe] in God be evil spoken of. For, "Woe to him by whose vanity my name is blasphemed among any." [Isaiah 52:5]- Ignatius, Epistle to the Trallians, Chapter 8 (Short Version - both versions available here)
Notice how, in this passage, Ignatius calls "faith" the "flesh of the Lord" and calls "love" the "blood of Jesus Christ." If he had said this about the bread and the cup, you might have thought he intended a transubstantial sense to his words. Here, however, you can plainly see that he does not intend such a sense. Instead, is employing metaphor.
Similarly, with Justin, the typical quotation is this (using the same article identified above):
"We call this food Eucharist, and no one else is permitted to partake of it, except one who believes our teaching to be true and who has been washed in the washing which is for the remission of sins and for regeneration [i.e., has received baptism] and is thereby living as Christ enjoined. For not as common bread nor common drink do we receive these; but since Jesus Christ our Savior was made incarnate by the word of God and had both flesh and blood for our salvation, so too, as we have been taught, the food which has been made into the Eucharist by the Eucharistic prayer set down by him, and by the change of which our blood and flesh is nurtured, is both the flesh and the blood of that incarnated Jesus" (First Apology 66 [A.D. 151]).
(I've likewise previously demonstrated that this quotation doesn't teach transubstantiation.)
And again, I can do more than simply point out that the quotation used doesn't teach transubstantiation. I can show that Justin viewed the Eucharist as literally bread:
And the offering of fine flour, sirs, which was prescribed to be presented on behalf of those purified from leprosy, was a type of the bread of the Eucharist, the celebration of which our Lord Jesus Christ prescribed, in remembrance of the suffering which He endured on behalf of those who are purified in soul from all iniquity, in order that we may at the same time thank God for having created the world, with all things therein, for the sake of man, and for delivering us from the evil in which we were, and for utterly overthrowing principalities and powers by Him who suffered according to His will. Hence God speaks by the mouth of Malachi, one of the twelve [prophets], as I said before, about the sacrifices at that time presented by you: 'I have no pleasure in you, says the Lord; and I will not accept your sacrifices at your hands: for, from the rising of the sun unto the going down of the same, My name has been glorified among the Gentiles, and in every place incense is offered to My name, and a pure offering: for My name is great among the Gentiles, says the Lord: but you profane it.' [Malachi 1:10-12] [So] He then speaks of those Gentiles, namely us, who in every place offer sacrifices to Him, i.e., the bread of the Eucharist, and also the cup of the Eucharist, affirming both that we glorify His name, and that you profane [it]. The command of circumcision, again, bidding [them] always circumcise the children on the eighth day, was a type of the true circumcision, by which we are circumcised from deceit and iniquity through Him who rose from the dead on the first day after the Sabbath, [namely through] our Lord Jesus Christ. For the first day after the Sabbath, remaining the first of all the days, is called, however, the eighth, according to the number of all the days of the cycle, and [yet] remains the first.- Justin Martyr, Dialogue with Trypho, Chapter 41 (link to source - most footnotes at source omitted above)
Notice how in this passage, Justin explains that the oblation of flour for the purification of leprosy pre-shadowed the bread of the Eucharist. And how the sacrifice of the bread and cup (for Justin) are a sacrifice of bread, similar to the oblation of fine flour in the Old Testament administration there. Notice as well that Justin views the sacrament as a "celebration ... in remembrance" but not a re-presentation.
In fact, we see this stated even more clearly in a later chapter:
But I must repeat to you the words of Isaiah referred to, in order that from them you may know that these things are so. They are these: "Hear, you that are far off, what I have done; those that are near shall know my might. The sinners in Zion are removed; trembling shall seize the impious. Who shall announce to you the everlasting place? The man who walks in righteousness, speaks in the right way, hates sin and unrighteousness, and keeps his hands pure from bribes, stops the ears from hearing the unjust judgment of blood closes the eyes from seeing unrighteousness: he shall dwell in the lofty cave of the strong rock. Bread shall be given to him, and his water [shall be] sure. You shall see the King with glory, and your eyes shall look far off. Your soul shall pursue diligently the fear of the Lord. Where is the scribe? Where are the counsellors? Where is he that numbers those who are nourished—the small and great people? With whom they did not take counsel, nor knew the depth of the voices, so that they heard not. The people who have become depreciated, and there is no understanding in him who hears." [Isaiah 33:13-19] Now it is evident, that in this prophecy [allusion is made] 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.- Justin Martyr, Dialogue with Trypho, Chapter 70 (link to source - most footnotes at source omitted)
Notice how Justin suggests that bread is given not as the flesh and blood as such, but rather in remembrance of those things.
4) Consider finally the absurdity of assuming that every time "[X] is [Y]" is used of things having two different substances, we should view this in a transubstantial sense.
1 Corinthians 10:4 And did all drink the same spiritual drink: for they drank of that spiritual Rock that followed them: and that Rock was Christ.
Will Mr. Rose try to suggest that the Rock was Christ in substance under the accidents of Rock? Surely no one would be so foolish as to make such a suggestion. May I further suggest to you that the only reason that you view the statement "This is my body" in a transubstantial sense is that you have been taught this tradition. It is not something found in the text or learned from it. Furthermore, the tradition itself is not a tradition that comes from the apostles. The historical evidence shows us that not only the term "transubstantiation" but the idea behind it were later developments, not the original apostolic teaching.