And he took bread, and when he had given thanks, he broke it and gave it to them, saying, ‘This is my body, which is given for you. Do this in remembrance of me.’ And likewise the cup after they had eaten, saying, ‘This cup that is poured out for you is the new covenant in my blood.’
Lutheran churchman Kenneth Howes writes on means of grace:
When Jesus refers to the Sacrament as ‘the blood of the new covenant’ or, as St Luke says it even more strongly, and as St Paul reports it, ‘the New Testament in my blood,’ we are told that this Sacrament is itself the Gospel, which we are physically ingesting. This Sacrament is nothing less than our salvation itself coming to us in an inexorable form, for our salvation if we believe, for our damnation if we do not.
I’d never thought about the words that way before, and I always was confused that Jesus called the cup the New Covenant itself rather than something like, I don’t know, blood, which you would expect if the statement was pure metaphor that drew on physical resemblance – incidentally, by not directly calling the wine ‘blood’, Luke also doesn’t say what a Romanist would hope. Given the parallel of the cup with the physical bread, there’s no way to escape the this referring to the sacrament and not to an absent future event. In some way, presence is real. In the sacrament, within that embodiment, we find the gospel, and in receiving it with faith we partake of Christ himself.
This is the point at which we must decide whether to believe in an omnipresence of Christ’s human body that allows its presence substantialiter or instead in a spiritual feeding on his body that, moving us through time and space (between the present and the first century, between earth and heaven, between the corners of the earth and Jerusalem), is more than metaphorical, more than a reminder. Or we can leave aside the Christological question (orthodoxy versus Nestorianism and Eutychianism, and the status of Calvin’s ‘finitum non capax infinitum’) for the moment and confess that Christ is truly in the Supper for God to declare us approved and accepted and redeemed.