This now illuminates for us the wonderful insight of the Sefas Emes as to why Mordechai and the other sages of the Sanhedrin established the celebration of Purim on the days that Yisrael rested from fighting their enemies. Those days are an essential, inseparable part of “mechias Amalek.” For, as explained, part of Amalek’s battle plan is to prevent Yisrael from resting. Thus, the true victory over Amalek is accomplished when we succeed in finding “menuchah”—rest and peace of mind—from the battles with them by clinging to Hashem’s Torah.
Hence, it is important to note that Chazal teach us that on Purim Yisrael accepted the Torah with “ahavah”—affection and devotion. This is taught in the Gemara (Shabbas 88a) in relation to the passuk (Shemos 19, 17):
"ויתיצבו בתחתית ההר, אמר רב אבדימי בר חמא בר חסא, מלמד שכפה הקב"ה עליהם את ההר כגיגית ואמר להם, אם אתם מקבלים התורה מוטב, ואם לאו שם תהא קבורתכם... אמר רבא אף על פי כן הדור קבלוה בימי אחשורוש, דכתיב קימו וקבלו היהודים, קיימו מה שקיבלו כבר". “And they stood under the mountain.” Rav Avdimi bar Chama bar Chasa said: This teaches that HKB”H held the mountain over them like an upturned barrel. Then He said to them: “If you accept the Torah, fine; but if not, your burial will be there.” . . . Rava said: Nevertheless, they accepted it during the times of Achashverosh, as it is written (Esther 9, 27): “The Jews fulfilled and accepted”—they fulfilled that which they had already accepted.
Based on what we have discussed, we can suggest that the Jews in the unwalled settlements, who were victorious on the thirteenth of Adar, fulfilled and accepted the Torah with “ahavah” on the day after the fighting was completed—on the fourteenth of Adar—in appreciation of the miracle. By accepting the Torah in this manner, they finally found a respite from the war with Amalek. In Shushan, however, the battle continued for one more day; so, they claimed victory over their enemies on the fourteenth of Adar. Thus, they fulfilled and accepted the Torah with “ahavah” on the following day—the fifteenth of Adar. With the power of the kedushah of the Torah, that is when they found a respite from the war with Amalek. This is why the two days of Purim were established on the days that the Jews rested from their battles with this enemy. On the day each accepted the Torah with “ahavah” respectively, they finally rested from the war with Amalek in the sense of (Bereishis 49, 15): "וירא מנוחה כי טוב"—and he saw a resting place, that it was good.
Nevertheless, even after the day of rest from the war with Amalek, our blessed sages still found it necessary to institute Shabbas Parah to purify Yisrael immediately after the days of Purim. As the great Rabbi of Apta, zy”a, explained, this was meant to cleanse Yisrael from the spiritual filth and tarnish that clings to them in every single generation as a result of the difficult battle with Amalek, who is the yetzer hara.
