1) The Torah warns against our imitating the laws and customs of Mitzrayim and Canaan. Rashi explains that these were the most barbaric societies to be found at the time. Ksav Sofer, however, takes the opposite view -- these were cultured societies, (supposedly)governed by laws and morals.
Sefer HaIkkarim writes that there is what is called "das tiv'it" and "das Elokit." You can have a society that has laws, that has a moral code, that is civil, but has no religion -- those laws are "dat tiv'it." On top of that, you can build a relationship with G-d through religious law and practice, which is "dat Elokit." (See also Derashos haRan in his derasha on parshas shoftim). Years ago when the j-blogsphere was more active you had a lot of people talking about "rationalist" forms of Judaism, which basically meant they wanted to turn everything into dat tiv'it. Religion in their view was a means to a more just society, a more ethical lifestyle. Hence, orthopraxy -- following the rules in deed because they made sense, but absent belief.
According to Ksav Sofer, this is what the Torah is warning against. Don't turn Judaism into ethics, into law, into a means for a civil society like you had in Mitzrayim, like you had in Canaan. Judaism is far more than that. "U'shamrten is chokosai v'es mishpatai... ani Hashem" -- observe the mitzvos in order to have a relationship with "ani Hashem," not just for the positive morals and ethics that are to be gained as well.
2) I have to mention a question of the Chasam Sofer that I don't understand, but which he feels is so strong that he leaves it with no answer and just says "mitzvah l'yasheiv." From the words "v'chai bahem" the end off the parsha we were just discussing ("U'shamrtem is chokosai v'es mishpatai asher ya'aseh osam ha'adam v'chai bahem" (18:5) the gemara learns that a person should violate an issur rather than die. For example, if a person is going to starve to death unless he eats McDonalds, then he should eat at McDonalds. The three exceptions to the rule are arayos, murder, and idolatry.
Chasam Sofer asks: the very next pesukim after "v'chaim bahem" talk all about the issurei arayos. How can arayos be an exception to the rule when it is the very context in which "v'chai bahem" appears?
I don't get it. "V'chaim bahem" is the conclusion to the parsha discussing the issur of chukos ha'aku"m and the command to keep our own chukim and mitzvos. Arayos is the topic of the next parsha. Who says one thing is connected with the other?
In fact, see Ba'al haTurim who writes that the juxtaposition of "lo tikrivu l'galus ervah" to "v'chai bahem" is to make the very point that even though there is a "v'chai bahem," nonetheless, "lo tikrivu" to arayos.
3) VaYidaber Hashem el Moshe achrei mos shenei bnei Aharon... VaYomer Hashem el Moshe...
Hashem spoke... and Hashem spoke. Why the repetition with nothing in the middle?
Rashi explains that there was something in the middle. "Achrei mos shnei bnei Aharon" is a message to be careful. Rashi gives a mashal: a doctor who tells a patient not to do X will likely be ignored; the doctor who says not to do X or you will die just like so-and-so has the patient's attention. Hashem wanted to make sure Aharon was on guard, so he warned that a mistake in doing avodah might lead to death, just as had occurred to Aharon's own two sons.
Is this not a great example of yiras ha'onesh? Don't be bad or Hashem will give you a big potch! Is this what it took to keep the great Aharon haKohen in line? Not only a threat, but even that's not enough -- a threat accompanied by an example he could relate to in order to make it real.
Wouldn't Aharon have listened to Hashem just because it was the dvar Hashem?
The mussar approach (e.g. see Ohr Yahel, Chiddushei haLev) is that we see from here that no matter how great the person, a human being is still flesh and blood, and while the neshoma may soar to lofty places, flesh and blood will always struggle with tayva, with failings, with challenges. No one is above the need for sometimes getting harsh mussar, the threat of a potch, because that is what our physical selves can relate to.
The approach of R' Tzadok and the Sefas Emes is quite different. Hashem's warning needs to be taken in context. As we discussed here, Nadav and Avihu were great people who aspired to a hisgalus of Hashem even greater than what Moshe merited. They could not contain their enthusiasm, their fervor, and so they entered the Mikdash and offered ketores even though they had no permission to do so and even though it would cost them their lives -- what value is human life relative to the prize of greater closeness to Hashem? (see Meshech Chochma in parshas Braishis on "V'h'yisem k'Elokim") For someone with that type of yetzer ha'ra, the threat of death is no deterrent -- the ends more than justify the cost. And yiras ha'romemus, appreciation of Hashem's majesty, awe of Hashem, is no deterrent either, as the greater one's appreciation, the more one would desire to come close to Hashem. In order to prevent Aharon from falling into the same trap as his children, Hashem had no choice other than to directly command Aharon and say that this is not the type mesirus nefesh that He sanctions, and it must be avoided.
For the ba'alei musar, the Torah is speaking to Aharon's frailties as flesh and blood like any one of us. For the gedolei chassidus, the Torah is speaking to Aharon's greatness, because who but a great person would be swayed by the temptation to even sacrifice his life to come closer to the majesty of Hashem.