In Arvei Pesachim, the tenth Perek of Masechet Pesachim, Rashbam and Rashi state that the main Mitzvah of Matzah is the Afikoman at the end of the seder. The reason that we recite the Berachah on the Matzah eaten earlier is based on the logic of Rav Chisda, who states: “LeAchar Sheyimalei Kereiso Meihem, Yachazor Viyvareich!?” “After he has filled up his stomach from them (Matzah) he will go back and recite the blessing on them!?” Rav Chisda refers to a case in which a person only had lettuce for both Maror and Karpas. According to Rav Huna, one should make a Borei Pri Haadamah when they eat the lettuce for Karpas, and then later make the Al Achilat Maror when they eat it for the Mitzvah of Maror. Rav Chisda disagrees, claiming that it is illogical to say the Berachah on the Maror later because of his aforementioned logic. Rather, both Berachot should be recited when the Karpas is eaten, and the Maror should be eaten later without a Berachah.
Rashbam and Rashi use Rav Chisda’s same logic to explain why the Berachah of Al Achilat Matzah is recited when first eating Matzah, even though it is not the main Mitzvah. Another example of this kind of logic is in regard to Tekiyat Shofar on Rosh Hashanah. There are two different times when Shofar is blown: Tekiyot DeMeyushav (sitting) and Tekiyot DeMeumad (during Shemoneh Esrei). The Tekiyot DeMeumad are the main fulfillment of the Mitzvah of Shofar. Nonetheless, the Berachah of Lishmoah Kol Shofar is recited before the Tekiyot DeMeyushav, because they are done earlier than the Tekiyot DeMeumad.
There appears to be a contradiction in the explanation of Rashbam. The Gemara at the beginning of Arvei Pesachim says that Rabi Yose permits eating all of Erev Shabbat and Erev Yom Tov, even close to sundown, because he does not require one to have an appetite for the Shabbat orYom Tov meal. On Erev Pesach, however even according to Rabi Yose one must not sit down to a meal on Erev Pesach once half an hour before Mincha arrives. Rabi Yose requires that one have a good appetite for the Matzah. Rashbam explains that since there is an obligation to eat Matzah, one should not eat the Matzah for the Mitzvah when he/she is full. The question is obvious: if Rashbam maintains that the main Mitzvah of Matzah is Afikoman, then the real Matzat Mitzvah is always eaten when full (it comes right after the main meal). What is the point of starving oneself on Erev Pesach when the only Matzah you will eat when hungry is not a Mitzvah anyway? On the contrary, it would appear that one is supposed to be full when eating the main Matzah; the Korban Pesach and the Matzah that goes with it were specifically eaten for dessert!
To resolve this contradiction, we must reexamine the statement of Rav Chisda. He never meant to say that a Berachah should be recited over a Devar HaReshut (optional Mitzvah). The Matzah that one makes a Berachah on is of course fulfilling the Mitzvah of Matzah, though not necessarily the full Mitzvah. Just because it’s not the main Mitzvah doesn’t mean that it is not a partial Mitzvah. Any time that one eats Matzah on the first night of Pesach he/she is fulfilling the biblical commandment of “BaErev Ttochelu matzot”. The same can be said for Shofar and Maror. Just because it is not the main Mitzvah doesn’t mean that one does not fulfill his/her obligation to hear the Shofar on Rosh Hashanah or eat Marror on Pesach. Even part of a Mitzvah is still very worthwhile.
-Adapted from a Shiur given by Rabbi Ezra Wiener at TABC