While discussing the debate about the nature of the Eucharist among the magisterial Reformers, Protestant James R. Payton wrote the following about Luther’s controversy with Zwingli, with the former accusing the latter of rejecting Sola Fide itself:
In Zurich Zwingli—who had come to a Reformation stance independently of Luther by reading the Scriptures and the church fathers—also ended up attacking transubstantiation, but as the elaboration of an idea not required by the scriptural text. Turning away from the medieval doctrine, Zwingli spoke rather of the bread as a symbol of Christ’s body, a symbol which helps recipients remember Christ’s suffering and death until he returns. Both these leaders had rejected transubstantiation, but they had nevertheless come to quite different assessments of what is received in the Lord’s Supper. By 1526 each had heard of the other’s views.
Luther denounced Zwingli’s views as mere rationalism (i.e., evaluating Scripture and its comfort in terms of reason) and thus of a piece with the objectionable medieval theological approach. For his part, Zwingli responded that Luther’s approach was itself an unpurged element of medieval sacramentalism, because it remained close to transubstantiation, (Luther had elaborated his position by urging that the body and blood of Christ were “in, with and under” the elements of bread and wine.) Thus Zwingli argued that Luther was holding on to aspects of the very medieval system he had written so powerfully against.
Luther bristled. He asserted that Zwingli’s approach was a return to “works-righteousness,” since the recipient does the remembering, and thus whatever grace may come in the Lord’s Supper comes because of that human remembering. This undermines justification sola fide—and so, of course, must be rejected. Zwingli countered that Luther’s attitude was a hangover from tradition, without biblical warrant and thus ultimately against sola scriptura.
Luther declared that Zwingli’s view attacked the Lord’s Supper and emptied it of grace, making it of no benefit to the recipient because it was simply another good work. Zwingli responded that Luther’s conception so filled the Eucharist with grace that everybody who partook, whether believer or not, received the body and blood of Christ. This, Zwingli averred, denied the very significance of faith itself. Luther did not back off from this challenge: even an unbeliever, he affirmed, indeed received and ate the body and blood of Christ!
Zwingli, Bucer and Oecolampadius were astounded. According to 1 Corinthians 11:27-28, some who are unworthy (i.e., believers who had not properly examined themselves and prepared for the Lord’s Supper) might thus “eat and drink judgment” on themselves. But, from Luther’s perspective, even a rank unbeliever receives Christ’s body and blood? Luther responded, “Yes, because Christ is truly there!” (James R. Payton Jr., Getting the Reformation Wrong: Correcting Some Misunderstandings [Downers Grover, Ill.: IVP Academic, 2010], 111-12)
Elsewhere (Ibid., 111 n. 13), Payton offers the following point which clarifies a popular misunderstanding of Zwingli’s understanding of the Eucharist:
It is a misrepresentation, though, of Zwingli’s view to describe it as a “real absence” of Christ from the Lord’s Supper; he did not hold to a merely symbolic or memorial view, even though that is what he articulated most clearly. For him, the “remembering” reflected the rich connotation of the Greek term anamnesis in which the “remembered” thing becomes present again. However, he never found a way to articulate this clearly, to indicate how God extends grace to those who appropriately receive the Lord’s Supper.
For excellent discussions of the debates about the Eucharist among the Reformers, see the relevant sections in:
Hermann Sasse, This is My Body: Luther's Contention for the Real Presence in the Sacrament of the Altar
George Hunston Williams, The Radical Reformation