i began thinking about it again in relation to John 6 and what's going on there. in the anglican prayer book service, i thought it said something like 'may the blood of our Lord Jesus Christ keep you in eternal life.'
in John 6.53-58 Jesus says
“Truly, truly, I say to you, unless you eat the flesh of the Son of Man and drink his blood, you have no life in you. Whoever feeds on my flesh and drinks my blood has eternal life, and I will raise him up on the last day. For my flesh is true food, and my blood is true drink. Whoever feeds on my flesh and drinks my blood abides in me, and I in him. As the living Father sent me, and I live because of the Father, so whoever feeds on me, he also will live because of me. This is the bread that came down from heaven, not like the bread the fathers ate and died. Whoever feeds on this bread will live forever.”
now, it's pretty clear that Jesus is talking about his death, but it's not insignificant that the same terms used to talk about his death are the used to talk about the remembrance meal he instituted.
Calvin says in the aforementioned treatise
The bread and the wine are visible signs which represent the body and blood, but the name and title body and blood are given to them because they are as it were the instruments by which the Lord distributes them to us. (Section 14)
we want to protect people from popery (check out not a couple of the 39 articles!), but what happens at the Lord's table isn't nothing either. Calvin does a great job of charting this line between Luther and Zwingli in this respect.
reading a couple of protestant commentaries on John 6 (Hendricksen and Köstenberg), neither think it's about the institution of the eucharist, but Köstenberg does suggest Calvin might be on to something in that it is derivative - that is, we celebrate what Jesus tells us about sharing in his death by sharing in the meal. indeed, whenever we remember Jesus' death on our behalf is a great opportunity to share in a remembrance meal, celebrating our union with him in his death and resurrection. we are not obliged to do it every time, but by never doing it we miss out on engaging all our senses (hearing, speaking, seeing, feeling, tasting) - a beautifully creaturely way for us creatures to join together to remember Christ's death, instituted by our creator!