Shevii Shel Pesach (the seventh day of Passover) is an unusual yom tov (Jewish religious holiday). Though it commemorates the extraordinary miracle of Keriat Yam Suf (splitting of the Red Sea), this theme is omitted in Emor and the other relevant parshiot in the Torah. Notwithstanding the significance of the miracle, this is the only yom tov in which the complete hallel is not recited, as it does not differ from the days of chol ha-moed with respect to its korbonot (sacrifices in the Holy Temple) (Arachin 10b). Indeed, this yom tov is completely subsumed under the broad rubric of Chag ha-Matzot (Holiday of Matzot, i.e. Passover) in parshiot Bo, Mishpatim, Emor, Pinhas, and Re'eh. While the Drishah (Tur, O.C. no. 490) cites the Maharil's view that one should formulate this yom tov in tefillah (prayer), kidush (sanctifying the day over wine), and birkat ha-mazon (grace after meals) as "yom simchatenu" ("the day of our joy") due to keriat yam suf, this position is almost uniformly rejected in favor of the continued emphasis of the exodus from Egypt and "zeman cherutenu" ("the time of our freedom").
There are also some indications that the shirah (song of praise) that followed the miracle may be as central to this yom tov as the event that inspired it. Indeed, the selection of a haftorah reading for this yom tov entirely ignores the specific occurrence of this day. Instead, the portion (Samuel II, 22) reflects the broader theme of shirah, faith, and gratitude. Perhaps, a brief examination of the phenomenon of shirat ha-yam (praise sung to God by the Jews after the splitting of the Red Sea) may further illuminate these emphases.
Shirat ha-Yam is written in a special formation in the Torah, underscoring its uniqueness. At the same time, its relevance is attested to by its inclusion in the daily prayers. While it seeks to commemorate a singular event, there are indications that its significance transcends its origins. The fact that a shirah did not follow immediately in the aftermath of the makkot (plagues) or even of yeziat mizrayim (exodus from Egypt) seems to underscore that it was not just a response to a supernatural experience. Moreover, the double introduction to the shirah- "va-yiru ha-am...va-yaminu" ("and the people feared...and they believed") requires clarification. The mention of Moshe Rabbenu in conjunction with Hashem is puzzling, as well. Having articulated their faith in Hashem, is it not superfluous or even inappropriate to affirm their belief in Moshe? The term "az" ("then") - implying a transition from, as well as a connection to, what preceded it suggests that the inspiration to express shirah constitutes an important juncture in the fledgling development of Klal Yisrael. Commenting on the future tense of "yashir" ("will sing"), Chazal view this moment also as a foundation for faith in the future destiny of the nation: "'shar' lo ne'emar ela 'yashir'...mikan le-techiyat ha-meitim min ha-Torah" ("it did not state 'sang', rather 'will sing'...from here we have a source in the Torah for the future resurrection of the dead") Furthermore, there is an interesting debate as to when the shirah begins: Tosafot in Sotah sees "az yashir" as an introductory sentence, while Rambam, hil. Sefer Torah, perceives it as first verse of the shirah itself. Rambam's intriguing perspective implies that Klal Yisrael's state of awareness is an integral aspect of the shirah itself!
Perhaps what differentiates this miracle and the response of shirah that it engendered was precisely the timing, as well as the order and emphasis delineated in the Torah that reflected a moment of spiritual clarity for Am Yisrael. The fact that the nation did not previously respond with shirah although they had frequently encountered supernatural manifestations, demonstrates that the shirah was more than a reaction to a superficial stimulus. The double introduction in which the theme of yirah (fear) preceded that of emunah (faith), after a period of deliberation and reflection implied by this series of pesukim, projects, at least momentarily, the spiritual maturity of Klal Yisrael It was indeed, "az", a moment of import, with implications for the application of the concept of emunah for the future- "shar lo neemar". Thus, according to the Rambam, the verse of "az yashir" constitutes not only the introduction but the beginning of the shirah! Moreover, it is consistent with this newly discovered broader perspective that at that moment, the nation finally fully comprehended the subtle critical role of Moshe Rabbenu. An understanding of the relationship between observing the mizvot- "zeh keili ve-anveihu" ("this is my Lord and shall glorify him"), especially as expressed in Chazal's doctrine of hidur miztvah (adorning the miztvah),- and acknowledging Divine intervention- "ashirah la-Hashem ki gaoh gaah" was critical at that special moment of keriat yam suf , but is no less pivotal in daily prayer.
The Torah chose not to formulate a separate yom tov commemorating keriat yam suf since the primary significance of this miracle was its impact on the concept of emunah and yirat Hashem that well transcended the event. The shirah that it engendered was possibly not less important than the physical salvation of Klal Yisrael. It is appropriate, indeed, that the last day of Chag ha-matzot, the anniversary of keriat ha-yam and the shirah, be fully integrated into the celebration of yeziat mitzrayim and "zeman cherutenu", as both the miracle of keriat ha-yam and the shirah that it inspired magnificently highlight the theme of emunah and hashgahah (Divine providence) that stand at the core of the significance of the exodus from Egypt (see Ramban, end of parshat Bo) and the integrated holiday of Chag ha-mazot.