One of Luther's big beef against the Roman church at the time (besides his newly found understanding of justification and righteousness) was over the practice of administering the communion. In fact, he seems to think that the error of the Roman church in this matter was so great that it gave "occasion for a schism in the church" (Luther The Pagan Servitude of the Church). There are three ways regarding the Eucharist in which the Church erred according to Luther:
[1] Giving only the bread and not the wine to the laity.
[2] Espousal of the doctrine of transubstantiation in Thomistic terms.
[3] Construal of mass as a good work or a sacrifice.
I don't have much to say about [1] right now, though Luther also believed that it is permissible to consume only one of the elements if one so chooses (but the laity should be permitted to consume both if they so wish).
Regarding [2], Luther's criticism of the account of transubstantiation as formulated by St. Thomas Aquinas is quite unfair. He charges St. Thomas of not only relying on Aristotle in matters of faith but also of misunderstanding Aristotle. Luther is definitely not a fan of Scholastic theology which made use of "the specious philosophy of Aristotle [which] took root in the church" (PSotC). It seems that for Luther, certain matters of faith cannot be comprehended through such analytic forms of reasoning.
One big problem is that Luther does not seem to properly understand St. Thomas' view. This is evident by remarks such as "Why could not Christ maintain His body within the substance of the bread as truly as within its accidents?" (PSotC). Anyone who is aware of Thomistic metaphysics involving substantial forms and the distinction between substantial and accidental changes can easily give a reply. Since my present concern is not over Thomistic philosophy, I'll let this one go.
So Luther adamantly maintains that what the priest is holding up is both fully bread and fully the body of Christ, and that we should believe this from a "simple faith".
Luther rejects [3] since he takes the mass to be a promise of God which we accept by faith (not works). Thus, it is not a good work nor a sacrifice (which is a kind of work) since it is something we receive (and not something we offer or actively perform). One point that needs to be made is that RC does think of the mass as a sacrifice, but it is not our sacrifice but Christ's sacrifice--the one and only sacrifice that is made present through the mystery of the Eucharist; and it is something we freely receive.
I do agree with Luther that there was a definite need of reform (whether the actual events in which the Protestant Reformation took place is justifiable is another question, one which I don't have an answer to). The unfortunate business with Tetzel (and in some ways, Leo X) involved what looked to be more like the desire for monetary gain as opposed to spiritual growth. As Luther states, "this sacred testament of God has been forced into the service of impious greed for gain by the opinions and traditions of irreligious men" (PSotC). This is what needed major reform (though in principle, I am not opposed to raising money for the creation of beauty--making money to build St. Peter's basilica is not in itself problematic). What was problematic was the acquisition of finances by the selling of indulgences. I actually have no problem with the system of indulgences (and my acceptance of Charles Williams' "substitutionary love" and St. Paul's claim of a mystical link that ties all the members of the body of Christ lead me to believe that something like the transference of the merits of Christ and saints is possible, with the appropriate conception of "merit" in play). However, such a system should not have monetary use; and RC eventually learned that lesson by proscribing the selling of indulgences (though not abandoning the distribution of indulgences altogether).
One final issue. Consider what Luther says here:
"Now the closer our mass resembles the first mass of all, which Christ celebrated at the Last Supper, the more Christian it will be" (PSotC).
Moreover, Luther is hesitant in accepting the doctrine of transubtantiation and the legitimacy of other sacraments since it has no Scriptural basis. Here are some of my concerns:
[i] Scripture does not describe every practice in detail, so it is hard to know if we are following the practice as completely as was performed by the disciples in Scripture. That is, unless one takes an extremely naive reading of many passages, there is much left out such that if we followed the practice as described in the text, our performance would not resemble the original practices at all (for instance, the part of the Lord's Supper that is described in the Scriptures was just a part of the entire passover meal, which is indicated by the fact that the cup which the Lord passed around was the 3rd cup of four in the Passover meal as indicated by St. Paul's claim that it is the "cup of blessing" and is followed by a hymn which the disciples sing afterward--thus, if we wanted to closely follow the early practice, we would have to engage in many activities not described in the text).
[ii] Luther seems to permit no room for development in doctrine or in practice here. Thus, we get an extreme form of Sola Scriptura (of which I will write about extensively at some future time). But why is there no such room? The forming of the canon seems to be a kind of development and innovation, along with the formulation of the doctrine of the Trinity (which brings us back to Luther's eschewing of Aristotle, which is odd since the orthodox conception of the Trinity heavily relies on Aristotelian [and more broadly, ancient Greek philosophical] notions such as substance (ousia, hypostasis), notions not found in Scripture). The question to ask is whether there is any permissible form of development and innovation apart from Scripture (and again, I will say more about this later).
[iii] Another thing to note is Luther's anti-ceremonialism and a desire to return to the "simplicity" of faith. I completely agree with Luther that the simple faith is what matters most. But it should not be the whole story. For instance, what matters most regarding my marriage is not that I buy my wife expensive jewelry or that we go on extravagant dates but that we genuinely love each other. And we can love each other simply and have no less love even when we are eating at McDonald's. However, one does not want to express that love at McD's but at a romantic walk on the beach under the moonlight. I could give my wife a ring from Cracker Jack as a token of our love, but I'd rather give her a diamond ring. Another way of putting it (cf. Thomas Howard) is to see ourselves as ceremonial by nature. We humans love to participate in ceremonies. We celebrate (or observe) birthdays, weddings, funerals, etc. And we form traditions that we like to follow, such as having a cake with candles, balloons, stockings, a white dress, black attire, flowers, etc. Part of being human is being traditional and ceremonial. These things may not be essential in a sense, but they are a natural and desirable part of being human.
[iv] Luther accepts paedobaptism (that is, infant-baptism), yet such a practice does not seem to have a Scriptural basis (at least, not a direct one--yes, yes, I know the arguments of paedobaptists such as its link to circumcision, etc.). So there seems to be, at least, a prima facie tension between Luther's acceptance of paedobaptism and his espousal of Sola Scriptura.
