Reference for Berakhot 41:6

איכא למפרך מה למזון שכן נהנה ומה לתורה שכן חיי עולם ועוד תנן על המזון מברך לאחריו ואינו מברך לפניו תיובתא:

One can, however, object to this reasoning : Why is Grace answered squired after a meal? Because it has been enjoyed. Why is a benediction required over the reading of the Torah ? Because it is life eternal. Moreover there is a teaching in our Mishnah: At his meal, he says the Grace after but not the Grace before ! The refutation [remains unanswered].

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