I have dealt with Robert Sungenis' arguments for the Mass as a propitiatory sacrifice and Transubstantiation from his book, Not by Bread Alone. In my discussions of these Roman Catholic dogmas, I focused on Sungenis' book so much due to it being the best defence I have encountered, and I believe in interacting with the best the other side has to offer. For some previous interactions with, and refutations of, Sungenis' arguments, see:
In the second edition of his book, Sungenis writes the following:
Protestant E. Svendsen adds another objection: " . . . what about the Last Supper, which is upheld by Catholics, as the original Mass? Was that a 're-presenting' of the sacrifice of the cross? How could it have been a re-presenting of something that had not yet occurred (Christ had not yet been sacrificed)?" (Evangelical Answers, p. 254, f. 4). The Last Supper is not a "re-presentation," nor has Catholic theology ever taught such. Rather, it is a presentation of what was to come, or the prototype of the re-presentation. Obviously, Jesus first had to institute or originally present the Eucharist in the Last Supper before His Church could subsequently represent it in the sacrifice of the Mass. Similarly, in John 20:22, Jesus does the same with the Apostles in regard to the reception of the Holy Spirit, Whom the Apostles receive on the Old Testament side of the cross prior to their reception of the Spirit at Pentecost. Likewise, Jesus institutes the sacrament of baptism on the Old Testament side of the cross (John 3:5-4:2) prior to its formal inauguration at Pentecost (Acts 2:38-39). All these events depend on the efficacy of the cross for their institution. In fact, they could not be instituted unless the cross was anticipated. Hence, Jesus institutes the Last Supper in the anticipation of the cross, as He makes plain in Lk 22:15, 20-22. (Robert A. Sungenis, Not by Bread Alone: The Biblical and Historical Evidence for the Eucharistic Sacrifice [2d ed.; Catholic Apologetics International Publishing, Inc.: 2009], 102-103 n. 103)
Notice that Sungenis admits that the Last Supper was not a propitiatory sacrifice. This shows that the Roman Catholic appeal to the language of the Last Supper (e.g., “this is my body”; the use of the participle form of “to shed/pour out” in Matt 26:28, both of which are discussed in the links above) cannot legitimately be used to support both the concepts of the Eucharist as a propitiatory sacrifice and Transubstantiation as such was not applicable to the Last Supper itself! This also contradicts Sungenis' argument later in the book, based on Matt 26:28 and the use of the participle ἐκχυννόμενον ("being poured out/shed") that "This would mean that the blood, at the time Jesus is speaking, is presently being poured out, that is, it is the blood of Jesus under the appearance of wine" (ibid., 127; emphasis in original).
