Musar for Megillah 35:12

We are told in 28,12 that Aaron was to wear the two gemstones on which the names of the twelve tribes were engraved on the shoulder-pieces of the ephod לפני ה' על שתי כתיפיו לזכרון, "on the two shoulder-pieces for remembrance before the Lord." This is an allusion to the events surrounding Purim of which we read in Esther 9,28 that "these days will be remembered and celebrated." This is a clear reference to the commandment to remember and never to forget what Amalek did to the Jewish people after they had crossed the sea and found themselves in the desert. The reason that the verse speaks both about נזכרים and נעשים is that the commemoration must precede the celebration. Even when Purim, i.e. the 14th of Adar, occurs on a Friday, so that the cities such as Jerusalem who celebrate Purim on the 15th of Adar celebrate it on the Sabbath, we cannot read פרשת זכות on that day, but must read it on the Sabbath preceding the 14th of Adar in order to comply with the sequence indicated in the Book of Esther. There is a dispute about this in Megillah 30 between Rav and Shmuel. The former holds that the paragraph commemorating the attack of Amalek on the Jewish people must be read in the Synagogue on the Sabbath prior to Purim, whereas Shmuel is of the opinion that it may be read even after Purim (i.e. the 14th). He reasons that since there are people who observe Purim on the 15th of Adar, in such an event the remembrance and celebration would coincide. In view of the fact that we accept the view of Rav, we need to understand why it is important to read פרשת זכור before the 14th of Adar.