We fulfill the mitzvah of zachor by reading the parshah of zachor on the Shabbos preceding Purim.
There are two mitzvos associated with Amalek. In Parshas Ki Seitzei the Torah writes, “Zachor es asher asa licha Amalek…” from which we learn that there is a positive commandment to remember what Amalek did to us when we left Mitzrayim. The Torah also commands us in the same section to wipe out any existence of Amalek – “Timcheh es zeicher Amalek.”
It is unclear from the Torah whether the mitzvah of remembering Amalek’s crime against us is a prequel to fulfilling the mitzvah of wiping out any existence of Amalek or if they are separate mitzvos. In other words, is there a mitzvah to remember what Amalek did to us even if it will not lead to the annihilation of Amalek?
The Rambam in his Sefer Hamitzvos (mitzvas asei 189) discusses the mitzvah of zachor. He writes that we must awaken our souls with these words (regarding Amalek’s crime) in an effort to wage war against Amalek. The Rambam concludes his explanation of this mitzvah by quoting an incident from Sefer Shmuel Alef. Shmuel Hanavi commanded Shaul Hamelech to wage war against Amalek, a fulfillment of the commandment of Timcheh es zeicher Amalek. Prior to doing this, Shmuel Hanavi recalled all the evil that Amalek visited upon the Jewish people when they left Mitzrayim. It is evident from this passage that the Rambam is of the opinion that the mitzvah of zachor is a prequel to fulfilling the mitzvah of timcheh.
The Sefer Hachinuch, mitzvah 603, writes that the mitzvah of zachor applies only to men, not women. He explains that this is because war pertains only to men. By using the laws of war to exclude women from the mitzvah of zachor, the Chinuch is revealing that he believes the two mitzvos are connected, and dependent. Zachor is a prequel to fulfill the mitzvah of timcheh. Therefore, one who is not obligated in timcheh is exempt from zachor.
The Minchas Chinuch is bothered by the ruling of the Sefer Hachinuch. Among many questions, he asks: How is anyone to know the reasons for Hashem’s mitzvos? We don’t know whether the reason for the mitzvah of zachor is to bring us to wage war against Amalek or if it is for some other reason – in which case, even after all of Amalek is completely annihilated, there might still be a mitzvah of zachor to remember what Amalek did to us. Similarly, women would be obligated to keep zachor even if they are exempt from timcheh.
Although the general way we fulfill our obligation of zachor is by reading the parshah of Zachor in Parshas Ki Seitzei on the Shabbos preceding Purim, the Magen Avraham (Shulchan Aruch, Orach Chayim 685) writes that one may also fulfill one’s obligation with the reading of the parshah regarding Amalek found in Parshas Beshalach, known as Parshas “Vayavo Amalek.” This is the parshah we read on Purim morning, before we read the Megillah. Therefore, if a person missed Parshas Zachor, he can make it up for it on Purim with the leining of parshas Vayavo Amalek.
The Mishna Berurah (685:16) argues with the Magen Avraham, and rules that one may not fulfill the obligation of reading Parshas Zachor by reading Vayavo Amalek. In explaining his opposition, the Mishnah Berurah cites a comment of the Ramban to Devarim 25:17 where he writes: “We must tell to our children and future generations what the bad people [Amalek] did to us and as a result we were commanded to wipe them out.” The Mishnah Berurah concludes that since the parshah of Vayavo Amalek lacks any mention of the war against Amalek, a person cannot fulfill his obligation of reading Parshas Zachor by reading it.
It would seem that the machlokes between the Magen Avraham and the Mishnah Berurah is dependent on the discussion we began with. The Magen Avraham is of the opinion that the mitzvah of zachor is independent of the mitzvah of micheyas Amalek. That is why he is not bothered by the fact that there is no mention of the war against Amalek in the parshah of Vayavo Amalek. He believes that there is a mitzvah to remember what Amalek did to us even if it will not lead to the annihilation of Amalek. The Mishnah Berurah, on the other hand, is of the opinion that the mitzvah of zachor is a prequel to fulfilling the mitzvah of micheyas Amalek. It is for that reason that he rejects the opinion that one can fulfill one’s obligation of Zachor by reading a parshah lacking mention of micheyas Amalek.