I saw someone explain that the command given to Bnei Yisrael not to leave their homes on Pesach night in Mitzrayim is because a person might be thinking it's the last night here in Egypt, let me go for a stroll and take one last look at the old neighborhood, let me grab a few memories for old times sake to take with me, etc. The person who thinks that way shows in his heart of hearts that he still is connected to the old neighborhood -- he feels some pain, even if only a bit, at having to leave. Hashem comes and says let that not be you. Leave b'simcha, with no regrets, no last look back.
I was thinking of that last night as everyone tries to get in a last pizza, a last morsel of chametz, before Pesach kicks in. It's like our last look back before we have to start on the matzah.
Rashi comments at the beginning of the parsha צו את אהרן – אין צו אלא לשון זרוז מיד ולדורות. Chasam Sofer explains that if something happens infrequently, it is out of the norm and it generates its own excitement. If the Mets were to make it to the World Series, everyone is interested, everyone is excited. If the Yankees make it, it's just the same old routine. When you have a command which is מיד ולדורות, that will continue for generations into the future continuously, then we need לשון זרוז so it doesn't become stale and boring, so that the excitment continues.
This is the question of the chacham at the seder. "Mah ha'eidus.... asher tzivah Hashem eschem." Pesach comes once a year and the whole house gets turned upside down. It's exciting! Why do you need tzivah = tzav לשון זרוז here?
To which we answer, "Ain maftirim achar ha'pesach afikoman," the taste has to stay with you. Today it's exciting because the whole house is covered in tin foil and we are sitting at a seder, but what about tomorrow when things are back to normal? What about the next day after that? How do you keep the taste in your mouth, how do you preserve the excitement?
This is the daunting challenge facing us on leil ha'seder and in reality, all year. The goal of v'higadta l'bincha is not just to tell a story, to give a speech like all the other speeches you give your children about what they should/should not do. It's v'higadta l'bincha... leimor -- the goal is to implant the message so that one day they can say it over to their children. The mitzvah of leil ha'seder is מיד ולדורות, so that taste will last for generations. "U'lfi she'hotzi atzmo min ha'klal kafar b'Ikar v'af atah." The "v'af atah" is the end of that sentence, not the start of a new sentence. The rasha was kafar b'Ikar and you sat by and watched and didn't try to do anything!? "...kafar b'Ikar v'af atah," then you are just as guilty as he is. The effort may not be successful, but at least you have to try.
So we try to fulfill V'higadta l'bincha as best we can, and if you want some chizuk, the Sanz-Klausenberger Rebbe says to look at the end of that pasuk. When we left Egypt we were spiritually in the sub-basement, below the ground floor, "v'at arom v'erya," lacking any mitzvos. Hashem gave us just 2 mitzvos to start with, pesach and milah, and that alone was enough to bring us to geulah. So when you face the disaffected "aino yode'a lishol" who is too disinterested to ask on his own, "at psach lo," start with something, "v'higadta l'bnincha leimor," saying whatever you can, and Hashem will give you siyata d'Shemaya from there. We then quote the end of the pasuk as proof: "...baavur zeh asa Hashem li b'tzeisi miMitzrayim," geulah started with our taking just a baby step of mitzvos, and Hashem jumped in and helped with the rest. So start with a baby step of teaching something, with a pesach maybe the size of a needle opening, and Hashem will take care of the rest.
Chag kasher v'sameich, and hopefully we will all get the siyata d'Shemaya we need to fulfill vhigadta and all the mitzvos haPesach properly.