1) Why is it the words of institution cannot be understood like in Mt. 13,38? There are passages which are understood without additional explanation figuratively.
2) Even if Jesus would really speak of a Real presence, why one can conclude that this is also true for the following Suppers which are celebrated?
3) What about the many passages which tell us that Jesus is now (physically) absent from earth?
4) At the first Supper: Jesus was without question with his deciples. How can he have meant that he would be at the same time with, in and under the bread? How can he physically be present on so many altars at the same time?
In 1 Corinthians 10:16 we are told that in the Lord's Supper the bread and wine do not represent the body and blood, but that there is "coming together" (Greek word koinonia) of the bread with the body and of the wine with the blood. In 1 Corinthians 11:27, the Corinthians were told that for them to eat the bread and drink the wine unworthily meant that they were guilty of sinning against the body and blood of the Lord. This makes it clear that the real presence is part of every celebration of the Lord's Supper.
Jesus is not physically absent from this world because he told us he would be with us always until the end of the world (Mt 28:20) and that where two or there are gathered in his name he is there with them (Mt 18:20). Jesus is not visibly present, but he is present.
His giving us his body and blood with the bread and wine is a miracle just like the many miracles he performed when he was on earth. No miracle is something we can reason out with logic (e.g., he was born of a virgin, he is both God and man in one person). But since Jesus promised he would do it, and since he is all-powerful (Mt 28:18), and since nothing is impossible for God to do (Lk 1:37), I simply believe his words.