Early Church Fathers
1 Greg. Naz. Ep. ad Procop., Graec., No. cxxx.
2 Harnack seems to know only the printed (and almost certainly incorrect) reading of the modern texts of the I. Apology (Chapter LXVI) where tou=to e0sti has taken the place of tou/testi. The passage did read tou=to poie=ite, ei/j te9n a,na/mnhsin mou, tou/testi to9 sw=ma/ mou; in which it is evident that the words"my body" are in apposition with tou=to and the object of poiei=te, which has its sacrificlal sense "to offer", as in the Dialogne with Trypho, o9 ku/rioj h9mw=n pare/dwke poiei=n (chapter xlj).
3 Harnack evidently does not fully appreciate the Catholic doctrine of the Sacrifice in the Holy Eucharist. No catholic theologian teaches that the essence of that sacrifice is to offer up the already present Body of Christ, but that the essence of the Sacrifice is the act of consecration; the "making the Eucharistic Sacrifice," as he accurately says, "whereby the common bread becomes the Bread of the Eucharist." Harnack says truly that "the sacrificial act of the Christian here also is nothing else than an act of prayer," but he does not seem to know that this is the Catholic doctrine to-day, nor to appreciate at its Cathoilc value the "Prayer of Consecration". The act of consecration is the essence of the Christian Sacrifice according to the teaching of all Catholics.