The Torah explicitly commands a blessing after eating — (Deuteronomy 8:10) states, "You shall eat and you shall be satisfied and you shall bless the Lord your God." But what about before eating? The text says nothing about that. So where does the obligation to recite a blessing before a meal come from?
Rabbi Yishmael, one of the foremost Tannaitic sages of the 2nd century CE, answered with an argument known as kal va-chomer — reasoning from the lesser case to the greater. His logic is elegant. If a person who has already eaten and is fully satisfied is still required to bless God, then how much more so should a person who is hungry and about to receive sustenance be obligated to give thanks?
The reasoning flips the expected order. One might assume that gratitude is a response — something you do after receiving a gift. Rabbi Yishmael argued the opposite. The moment of need is actually the greater moment for blessing, because the anticipation of God's provision is itself worthy of acknowledgment.
This teaching from the Mekhilta de-Rabbi Yishmael, the Tannaitic midrash on Exodus, became a cornerstone of Jewish liturgical practice. The entire system of berakhot (blessings) recited before eating — over bread, wine, fruit, and all other foods — traces its scriptural logic back to this deduction.
A person who waits until after the gift to say thank you has good manners. A person who blesses before receiving the gift has faith.