We say in the haggadah, "Ilu kara lanu es ha'Yam v'lo he'evireinu b'socho b'cherava - dayeinu." Everyone asks: what would have been the point of splitting the sea if not for us to cross it on dry land (see Netziv)?
The Sefas Emes (5631) explains that to turn the sea into dry land or dry land into sea is a miracle, but the miracle of Yam Suf is bigger than that. The great miracle of Yam Suf was that Bnei Yisrael went "holchim b'TOCH haYAM ba'yabasha" -- the sea remained a sea, and nonetheless, we walked through it on dry land. There are some religions, and some people who thing this is what our religion is all about, where everything is about cloistering yourself from the world, striving for some spiritual, mystical state of ecstasy that is completely divorced from reality. When the waters of materialism rage around you, you build a teivas Noach to hide in and escape to. And then you have people who want none of that, people who are so tied up with the affairs of olam ha'zeh that they have no time for anything spiritual. Yam or yabasha, either/or, take your pick. Our mission is to be b'toch ha'yam, to live in the world, to have a connection with things around us, but at the same time, to be ba'yabasha, to not let the waters raging out there influence us.
Ilu he'evireinu b'socho b'cherava -- it would have been enough for Hashem to drain the water of the Yam for us to cross and dayeinu. But to be able to walk through the sea, that is above and beyond.
"Va'yitzaku Bnei Yisrael el Hashem," (Shmos 14:10) Klal Yisrael cried out to Hashem while they stood on the banks of Yam Suf. Rashi comments that "tafsu umnus avosam b'yadam," they took to the craft of their forefathers, as we find that the Avos prayed to Hashem. The meforshei Rashi ask (e.g. see Gur Aryeh) why it is that Rashi comments only here that "tafsu umnus avosam" and not on any earlier other pesukim that speak about Bnei Yisrael crying out to Hashem, e.g. "Va'yeianchu Bnei Yisrael min ha'avodah va'yizaku?" (2:23)
Tiferes Shlomo answers that uman = a craftsman, someone who can shape raw materials into something new according to his desire. The lesson of Yam Suf, which is why Rashi makes the comment davka here, is that teva is raw material that can be bent to our will just like an uman can manipulate raw materials according to his will. We control the world around us; it does not control us.
2) Many people already have written about the seder being the opportunity to teach emunah to our children. The culmination of pesach and that whole process is the last day(s) and kri'as Yam Suf. Recall earlier this year when we discussed the chiddush of the SHL"H that ideally one should sing shirah in anticipation of a miracle, with emunah in the outcome, not wait for it to happen (R' Chaim Brisker held otherwise). "Ya'yaaminu b'Hashem ub'Moshe avdo -- Az yashir Moshe..." Sefas Emes (5635) writes that it was not seeing the splitting of the sea that triggered Klal Yisrael to sing shirah, but it was reaching the heights of emunah, "ya'yaaminu ba'Hashem," which then led to "az yashir..."
3) Simcha vs. Shirah:
'enough' had He not continued to 14:22 from :21, owing to a change of heart (Rashi, 14:19a, din*); the decision of Dayan haEmes would suffice.
*the end of pasuk 14:21, when dry land appears >before< the water splits, betrays confusion in the Divine Mind, hinting at a Conceivable, late hour cessation of Mercy.
seems an oblique interpretation from Tiferes Shlomo, since Hashem is the "raw material" that we would manipulate by the craft/tool of prayer, not "teva". moreover it's at "2:23" that bnei Yisrael are physical craftsmen, shaping clay into bricks and bricks into storehouses, per the posthumous will of the Egyptian king.
the "lesson" is that "[w]e control the world around us" when we put Hashem in charge; "raging" materialism controls us, whenever a Paro rules.
so why does Rashi delay his comment?Delete
at 2:23, with Paro newly dead, the klal is newly hopeful to catch a break. a natural (material) opening in circumstances hardly calls for prayer, any groan will do, if needed at all.
at the yam, there is no natural opening for bettering the situation-- time for a well-crafted cry...