It is certainly clear enough, and really beyond any reasonable doubt, that Luther and Chemnitz were "consecrationists." That is to say, they consistently taught and confessed that, by and with and at the speaking of the Verba, the bread becomes and is the Body of Christ, and the wine becomes and is the Blood of Christ. It is the Word and work of the Lord Jesus that does this and gives this. As Herman Sasse, Tom Hardt, Bjarne Teigen, Scott Murray, John Stephenson, et al. have pointed out, this "consecrationist" theology of Luther and Chemnitz flows from and with the doctrine of justification and the authority of the Word of God. It is not only what I was taught, or at least understood, from my seminary professors, but what I have always understood and believed from the Words of Christ Jesus, my Lord. And, as it is the clear teaching of Luther and Chemnitz, it is likewise clear that "consecrationism" is the teaching of the Formula of Concord, which was authored chiefly by Martin Chemnitz (echoing much of what he wrote in his Examination of the Council of Trent), and which explicitly cites Dr. Luther as the foremost interpreter of the Augsburg Confession.
It is also clear and straightforwardly obvious, that Walther and Pieper, following the 17th-century Lutheran scholastics, were "receptionists." That is to say, they taught that the Body and Blood of Christ were present only in and with the actual eating and drinking, and neither before nor after nor apart from that eating and drinking. This "receptionist" teaching follows from the emphases of Melanchthon, which stood in tension with Luther's emphases while both men were still alive, but which developed and sharpened in Melanchthon, in his students and beyond, in the years following Luther's death. Resulting controversies over a right understanding of the axiom, that "nothing has the character of a Sacrament outside of its intended use," were addressed by the Formula of Concord. However, in spite of the Formula's clarification, and in spite of Luther's and Chemnitz's understanding and explanation of the axiom in question, subsequent generations of Lutheran scholars adopted and taught a "receptionist" interpretation of the axiom, and, therefore, of the Sacrament. This view was fostered and solidified by a reliance on Aristotelian philosophy, or, rather, on a misunderstanding and misuse of Aristotle's "four causes." Walther and Pieper followed the Lutheran scholastics in this vein, and read back into Luther and Chemnitz and the Formula of Concord that "receptionist" view, which came to predominate.
It is a daunting thing to be in the position of saying that Walther and Pieper (and the 17th-century Lutheran scholastics) were wrong, but, on this point, they were. I'll stand with Luther and Chemnitz vis-a-vis Walther and Pieper, eight days a week. Even more important and to the point, I'll stand with the Words of our Lord Jesus Christ against anything and everything else in heaven and on earth. What He speaks, is so. It is, at once, the most profound Mystery and the simplest thing imaginable.
To answer the question that was put to me at the end of my presentation: No, I don't think that Walther and Pieper were Zwinglians, and I have no desire or intention of making any such claim. They certainly taught and confessed that the true Body and Blood of the Lord Jesus Christ were received and eaten with the bodily mouths of the communicants, and in this faithful confession they were as far from Zwingli as the heavens from the earth. But in their "receptionist" position, they weakened and undermined the fundamental power and definitive authority of the Word of Christ, and allowed human philosophy and participation to intrude upon the Mysteries of God. It was one of Pieper's famous "felicitous inconsistencies" that preserved their faithful confession of the "Real Presence" alongside their "receptionism." Perhaps in largest part because their practice preserved a care and reverence for the consecrated elements that belied their theoretical teaching on the presence. Carefully consecrating only as many elements as would be needed for the Holy Communion, but also using a second consecration whenever additional elements were required to complete the distribution, and then consuming any and all remaining consecrated elements, rather than ever mixing consecrated with unconsecrated elements, made a strong ceremonial confession of the central and definitive significance of the Verba-consecration.
In subsequent generations, a breakdown in practice, supported and defended by an appeal to "receptionism," has eroded confidence in and reverence for the Verba and the Body and Blood of Christ. Thus, the historic Lutheran doctrine and practice spiral downward together.
In saying that Walther and Pieper were wrong on this point, in deference to Luther and Chemnitz and our Lutheran Confessions, and above all in deference to the clear Words of Christ, I do not dishonor those faithful men, who were far stronger and much better theologians than I am. But those who would appeal to Walther and Pieper (over against Luther and Chemnitz) in defense of a careless, sloppy, or otherwise irreverent practice, do those men a grave injustice. Worse is the dishonor that is perpetrated against the Word and Sacrament of Christ, our Lord.