I
In the period between Purim and Pesach, it is instinctive to analyze a passage in the Talmud which deals with both holidays. The Gemara says in Megillah (14a), "If shira was said when we were delivered from slavery to freedom at yetzias mitzrayim, then when we are delivered from death to life we must certainly say shira". This is the source for the mitzvah of reading the megillah on Purim, and would obligate us to say Hallel on Purim if not for three technical reasons that the Gemara lists.
Rashi adds that Hallel is shira and the shira of yetzias mitzrayim is Shiras Hayam. This means that Shiras Hayam teaches a halacha for all generations, i.e., if Am Yisroel is delivered from a threat to its life, there is an obligation to say Hallel.
An obvious question can be raised. The Shiras Hayam describes supernatural miracles. But on Purim, no laws of nature were broken. How then can the Gemara derive the obligations of Purim from yetzias mitzrayim? Perhaps only miracles which break natural law obligate us to say shira, but not hidden miracles like those of Purim. In addition, the Gemara in Megillah 10b asks a second question. The angels wanted to say shira the night that the miracle of kriyas yam suf occurred, but Hashem said, "My creatures are drowning in the sea, and you want to say shira?!" Now, if the angels were told not to say shira because the Egyptians were drowning, then why do we say shira? And why do we read the Megillah on Purim?
The Meshech Chochma (Shemos 12:16) answers as follows: "Purim is not celebrated on the anniversary of the victory against our enemies. Am Yisroel does not rejoice over the downfall and death of its foes. We celebrate Pesach because we were saved, not because our enemies perished, and we rejoice and read the Megillah on the day that we rested, the day after the war, when no one died, but we were saved.
For this reason, Hashem included the command to observe the seventh day of Pesach among the mitzvos given to us before we left Egypt, even though the mitzva did not apply in Mitzrayim. Hashem did this to show that the holiday is not to commemorate the drowning of the Egyptians, as its observance was commanded prior to the historical event. It follows from the Meshech Chochma's idea that the Shiras Hayam, which we read on the seventh day of Pesach is recited over our deliverance, and not because of the death of our enemies.
We can now answer the first question as well. Should the Shira be required because of the downfall of our enemies, we would not be able to derive Purim from Pesach. After all, the Egyptians were killed by miraculous events culminating with keriyas yam suf , whereas Haman and his followers were destroyed by natural means.
In reality, however, the Shira is required only because we were saved from our enemies. In this context, what is important is not how our enemies perished, but how great the threat against us was. Therefore, if we said shira when we were saved from slavery, we must certainly say shira when saved from death.
II
We do not recite the full Hallel on the seventh day of Pesach. The Gemara in Erchin (10b) explains that Pesach differs from Sukkos, when Hallelis said every day, because on Pesach the same Musaf offering is brought each day, whereas on Sukkos each day has a different Musaf. However, the Medrash says that Pesach differs because on the seventh day we cannot say full Hallel, since the Egyptians drowned. It would be wrong to recite full Hallel on Chol Hamoed and not on the seventh day which is Yom Tov, so it is omitted on all days after the first.
The Medrash seems to contradict the Gemara, as it gives a different reason as to why we do not say full Hallel. Many answer as follows: the Gemara explains why Pesach's status as a Yom Tov does not obligate us to say Hallel even on the seventh day. The reason is that Pesach is one long Yom Tov, and therefore does not require a new recitation of the full Hallel each and every day, whereas Sukkos is eight different Yomim Tovim, each of which warrants a recitation of the full Hallel. The fact that the Musaf is identical all seven days of Pesach but changes each day of Sukkos indicates this distinction.
The Medrash relates to a different issue: why we do not say Hallel because of the miracles of Kriyas Yam Suf. The reason is that when Hashem's creatures drown in the sea, we should not say shira.
Two questions remain. One, why then did our ancestors say shira? And two, why do we sal Hallel on the first night of Pesach even though our enemies died?
We can answer this question based on a comment of the Netziv. The Chasam Sofer writes that Hallel on Chanukah is a Torah obligation, as evidenced from the Gemara which derives the mitzva to say Hallel from Shiras Hayam. The Netziv quotes the Gemara in Berachos (14a) that Hallel is a rabbinic commandment. How can we reconcile this statement in Berachos with the Gemara's proof from Shiras Hayam that Hallel is a Torah obligation?
The Netziv writes that the Torah obligation exists only when the miracle occurs. On the subsequent anniversaries, the obligation is rabbinic.
The Rabbis did not introduce Hallel on days when our enemies died. Therefore, there is no full Hallel on the seventh day of Pesach. Only Purim, which is celebrated on the following day could have qualified as a day of Hallel.
Our ancestors recited Hallel when the sea split because at that point Hallel was a Torah obligation which had to be discharged even though our enemies dies on that day. On the first night of Pesach we must consider ourselves to have just left Egypt at that moment (as ruled by the Rambam). Therefore, there is a Torah obligation to say Hallel, an obligation that overrides the problem that arises because our enemies died that night. And so the Shira, which is like full Hallel, was said when the sea was split, and full Hallel is said every year on the first night of Pesach but not on the seventh day.
Unfortunately, death threats made by the enemies of Am Yisroel, especially in Eretz Yisroel are not a thing of the past. As we celebrated Purim this year, we were effected by the recent murder of innocent Jews by vicious enemies, and the continued threat to our security. We pray to Hashem to deliver us from the threat of death to a life of peace, not because we want our enemies to be destroyed but because we want to be saved.
The Medrash teaches us that the Shiras Hayam is similar to the Hallel we will all sing when the final redemption comes. May we be privileged to join in that great song- bimhera beyameinu - Amen.