Our first reading gives us Paul's account of what Jesus said over the bread and wine at the Last Supper.
There is a difference between what Paul wrote in Greek and the way we translate Paul's words in our English Bibles and in our Mass. Paul. in his actual Greek account used the Present tense, saying, "this is my body which is for you," and "this is my blood which is poured out for you."
Our English Bibles change Paul's words to the Future Tense, writing, "The is my body which will be given, which will be poured out."
Our church's reason for changing those tenses seems to be that we like to see Christ's sacrifice as
enacted as only the death on the cross.