I agree with the basis of your point - that Jesus speaks and we, for all time and eternity, reply amen - surely, indeed, truly, let it be. But, just as in the example Paul gave to the Corinthians about someone speaking in an unknown tongue in the assembly of believers and then having no one there to interpret what the person said, he said that tongues-speaking person should keep silent, because no one there would be able to give them an "amen" for their words if nobody knew what was said (I Cor. 14).
Therefore, for us to say "amen" to anything, we need to understand what it is we are agreeing to. When Jesus had that last Passover meal with his Apostles, he took the bread - which was the third piece that was hidden under the cloth (Of the three matzoes, the middle matzah on the Seder plate is broken in two. The larger part is put aside for later use as the "afikoman" which is hidden in a napkin. After the meal, the half-matzah which had been “hidden,” set aside for the afikoman (“dessert”), is taken out and eaten. It symbolizes the Paschal lamb, which was eaten at the end of the meal.). It is this piece that he broke and handed out telling them, "This is My body which is given for you; do this in remembrance of Me." (Luke 22:19). The symbolism could not have been more precise - because he was telling them that HE was the Messiah that all the Passover observances in the past were done to remember HIM and his coming to be the lamb of God who takes away the sins of the world.
When he said of the bread, "This is my body.", he was holding up a piece of that hidden third unleavened bread and he revealed to them that it was his body, that like that bread, would be broken for them (and the world) the very next day - only they didn't know that yet. The incomprehensible mystery is that ALL the feasts and holy days and sacrifices in the past of the Jewish people were being fulfilled BY him that very time! The bread didn't need to physically or spiritually or literally change to Jesus' actual flesh and blood and I believe they all there knew that. Jesus certainly didn't have to go into detail to explain to them what he meant - they got it. JUST as they got it when he first spoke of it as recorded in the gospel of John (because God had given it to them to see).
His "once for all" sacrifice doesn't need to be made present or re-presented, because by that one sacrifice he perfected FOREVER those that come to him in faith. The observance we do is to remind - or to keep ever before our faces - the love of God that was so great He gave His only begotten son that whosoever believes in him will NOT perish but HAVE everlasting life. That truth is so amazing and so awe inspiring that we CAN only say AMEN - let it be, so be it, verily, truly, YES GOD.
Hope you have a blessed rest of the week.
The Passover was a foreshadowing of Christ.
He was simply explaining the meaning of what they had been doing for so long without understanding the fulfillment, that fulfillment which was sitting before their very eyes.
At that point, the symbolic foreshadowing before the fact, became a symbolic remembrance after the fact.
Thanks, boatbums. Same to you.