I think your reference to the Didache regarding repentance required to make “your sacrifice” “undefiled” only makes sense in terms of the traditional Protestant view that Christians on a daily basis need to surrender themselves to Christ as a living sacrifice. The bread and wine are not the sacrifice now. WE are. Thus Christ said we should pick up our cross (ie, die to the world) daily and follow him.
I'm sorry, but you cannot say that that is the "traditional Protestant" view because the Lutherans believe in the True Presence of Christ in the Eucharist. As Martin Luther said Who, but the devil, has granted such license of wresting the words of the holy Scripture? Who ever read in the Scriptures, that my body is the same as the sign of my body? or, that is is the same as it signifies? What language in the world ever spoke so? It is only then the devil, that imposes upon us by these fanatical men.
One cannot say that this is only the daily surrendering to Christ -- btw, that is in orthodoxy (from which the non-orthodox took) but is not "only" -- the reference in the Didache to an undefiled sacrifice says "offer the Eucharist" which is the sacrifice referred to in the following