Achrei Mos, Vayikra 18:5. וָחַי בָּהֶם, Vachai Bahem: The Obligation to Preserve Life Countermands Other Religious Obligations

וּשְׁמַרְתֶּם אֶת חֻקֹּתַי וְאֶת מִשְׁפָּטַי אֲשֶׁר יַעֲשֶׂה אֹתָם הָאָדָם וָחַי בָּהֶם  אֲנִי ה
Observe my ordinances and laws, that man shall do them and live; I am Hashem.

The Gemara in Yoma 85 says that the words "vachai bahem" in this passuk teach that the obligation to preserve human life overrides the obligation to observe other Mitzvos.  If the only way to preserve life is to transgress a religious prohibition, the preservation of life is dominant.

This is true for almost all the aveiros in the Torah.  A man who is starving should eat treif food; a man whose life is endangered should be mechallel Shabbos to protect himself.  But there are three exceptions (Pesachim 25 and Sanhedrin 74a):  Avodah Zarah, Gilui Arayos, and Shfichas Damim.  If a person is given a choice- worship this idol or we will kill you; engage in an illicit sexual relationship or we will kill you; kill that other man or we will kill you, one must submit to martyrdom rather than do the prohibited act. 

The Chasam Sofer points out an odd thing.  The source for the rule that life outweighs other religious considerations is our passuk, Vachai Bahem.  This passuk introduces the parsha of Arayos, of forbidden sexual relationships.  Why is it that this almost-universal rule of Vechai Bahem, the rule of Ya'avor ve'ahl yei'hareig, is taught in the introduction to the parsha of Arayos, when Arayos is one of the three rare exceptions to the rule?  Ve'chai Bahem could have been stated in 98% of the Torah in a context where it applies.  Why was it incongruously stated here, where it does not?

The Chasam Sofer does not answer his question: he says "mitzvah le'yasheiv," it would be a mitzvah to explain it.

It's mitzvah time!

First of all, I want to point out that Tosfos, I think, noticed this oddity.  Tosfos in Sanhedrin 60a, d'h חקתי דהשתא, says that despite the contiguity to the parsha of Arayos, the words וָחַי בָּהֶם in this passuk are not talking about Arayos but rather about the 613 Mitzvos of the Torah.  Tosfos does not say what it is about those words that made  him say that, so it's not absolutely clear that Tosfos means what the Chasam Sofer means.  It is possible that Tosfos might just be saying that the idea of vechai bahem is so broad a concept, that it must be referring equally to all the taryag because all the taryag bring life, and it has not specific association with any one parsha.  But it is more probable that Tosfos means the din of pikuach nefesh, that the fact that din of pikuach nefesh that is learned from וָחַי בָּהֶם does not apply to Arayos is proof that this passuk is talking about the whole Torah and not about Arayos. 

Reb Meir Simcha here in his Meshech Chochma talks about this passuk and the Tosfos, and he says that Tosfos means the din of Pikuach Nefesh, the Chasam Sofer's point.  This is no taina on the Chasam Sofer, for two reasons.  1. He probably learned Tosfos not like Reb Meir Simcha, but instead like the first pshat I said above, and 2. as I said before, even when we accept that the passuk is not talking about Arayos, it's odd that it's in the introduction to Arayos. 

In any case, Reb Meir Simcha initially suggests that the din of vechai bahem / yaavor ve'ahl yeihareig does apply to Arayos in cases of lo sikrevu legalos erva, i.e., Clintonesque contact without znus mamash, where it's only a lahv.  However, Reb Meir Simcha points out, this is not true according to the Rambam, who holds that even abizraihu of AZ GA and ShD is yeihareig, even tiny issurim of arayos are yeihareig ve'al yaavor, as stated in the Gaon in YD 157 (and, if I remember correctly, as discussed at length in the intro to Sefer Hamitzvos).   But then he says that according to Reb Meir, in Sanhedrin 59a, that even a Goy that is osek batorah is like a kohen gadol, and Reb Meir bases it on our passuk- Ha'adam vechai bahem- not Yisrael, but any Adam- then we can say that since Goyim are not chayav in Kiddush Hashem (Sanhedrin 74b), if they would have a case of oneis by arayos, their halacha would be ya'avor.  I'm not sure why he says this only in Reb Meir.  The din that pikuach nefesh is doche the seven mitzvos Bnei Noach, I assume, is agreed to by everyone, so it's not only Reb Meir that holds that vechai bahem also goes on Goyim. 

So: Reb Meir Simcha's teretz on the Chasam Sofer's question is: only for Jews, who have a mitzvas Kiddush Hashem, do we limit Vechai Bahem from applying to arayos.  For Goyim, who do not have a mitzvas kiddush Hashem, the general petur of Vechai Bahem applies even in cases of Arayos (and Avodah Zara, but not Retzicha, as Reb Meir Simcha says in the Ohr Sameiach, 5 Yesodei Hatorah 6.)  So we can say that the passuk is in the parsha of Arayos because Goyim are also metzuva on Arayos, and for Goyim, Vechai Bahem is docheh even issur Arayos.

So we have Reb Meir Simcha's answer, two tentative approaches of my own, Chaim B's teretz, and a drush teretz:

1. Reb Meir Simcha in the Meshech Chochma: These words apply to non-Jews as well as Jews, and although we, Jews, cannot apply them to the three chamuros because of our Mitzva of Kiddush Hashem, Goyim do not have a mitzva of Kiddush Hashem, and so for Goyim, the וָחַי בָּהֶם dispensation does apply to Arayos and Avoda Zara.

2. My first tentative teretz: That Vechai Bahem does apply to Arayos.  If one would be weak and would choose to do the aveira and save his life, he would not be chayav missa, as almost all the rishonim (Tosfos, Ran, Ramban, Rambam in Yesodei Hatorah) say in the sugya of Abaya and Rava on mei'ahava umei'yira.  Why would he not be chayav missa?  Because Vechai Bahem removes the chiyuv missa, even if it remains assur.

3.  My second tentative teretz:  The Mishna Sanhedrin 73a says that if we see a man running after a person to kill him or running after an erva for an illicit sexual act, we kill the pursuer, the rodef.  The Rif at the very end of Eilu Ovrim in Pesachim says that you can kill a rodef even on Yom Kippur or Shabbos, although wounding, to say nothing of killing, any living thing is an issur de'oraysa.  The Mishneh Lemelech at the very end of Hilchos Shabbos, 24:7 brings this Rif; he says that while the Rif makes it clear that you can kill a murder rodef on Shabbos, what about killing an arayos rodef on Shabbos?  He doesn't state a final opinion.  I would say that we would be mattir chillul shabbos to kill an arayos rodef on the basis of vechai bahem.  This would explain what it's doing in this parsha.  (But I don't get the Mishneh Lemelech.  If you can kill a murder rodef on Shabbos, that's because of the din of pikuach nefesh.  Why would arayos rodef be different?  What happened to "kaasher yakum ish ahl rei'eihu urtzacho nefesh kein hadavar hazeh?)

4.  See the comments; Chaim B shtells tzu Reb Elchanan's pshat in Tosfos in Kovetz He'aros #48.  He pulled the rug out from under me on this.  I should have thought of what he said, but that's the breaks.  Here's what Chaim wrote:
R' Elchanan explains that Tosfos holds that pikuach nefesh is not nidche because of the big 3. Pikuach nefesh (or v'chai bahem) still applies, but it clashes with the chiyuv to be moseir nefesh. Net result is shev v'al ta'aseh.

 5.  I copied this from HaRav Yissachar Frand, because he writes better than I do.
A cursory examination of this pasuk would seem to indicate that the Torah is telling us that human life is more precious than keeping the mitzvos. Therefore, if you have a choice between observing Shabbos or staying alive, your life is more valuable than the mitzva. We would conclude that there is a general rule: life is more important than the mitzvos, with just three exceptions.
 Rav Moshe Feinstein Zt"l, in his sefer "Igros Moshe," writes  that this common understanding of the pasuk is incorrect. That is not what the pasuk is saying. The true explanation is as basic as a Targum Onkelos.
The Targum Onkelos translates this pasuk as: "and you should live through them in the World to Come." In other words, the pasuk is not telling us to stay alive and neglect the mitzvos, because life is more precious than mitzvos. The pasuk is telling us that the most precious thing in life is keeping mitzvos, because they bring us to olam haba, the World to Come.
Therefore, if I have a choice between observing the Shabbos or being murdered, the Torah says, "live!" Why? Not because life, for its own sake, is more precious than G-d's Commandments. Rather, life is precious because you can do those Commandments! Therefore, perform work on this Shabbos so you can keep so many more Shabbasos in the future. Eat chometz on Pesach. Why? So you can go on and do more mitzvos, and be worthy of life in the world to come.
This is an entirely different perspective. Life is not valuable just for the sake of life itself, without a purpose. Life is not valuable simply in order for a person to work, do errands and go to ball games. That is not what makes life worth living! What does make life worth living? "V'chai bahem" - "l'chayei alma" [in the world to come]. Life that leads to this goal is worth living. The Torah is instructing us to violate the Shabbos and to eat chometz [leaven] on Pesach. Why? The reason is because a human life is valuable because it can do so many more mitzvos in this world. Therefore, violate the Shabbos once so that you can observe Shabbos many more times. (end quote)

Based on this approach, the answer to the question is that Vachai Bahem is in fact universal.  The application of Vachai Bahem, however, varies.  In most cases, the application of vachai bahem results in overturning the issur in order to live.  In some cases, though, the application of vachai bahem results in giving up one's physical life, because doing the issur would cause terrible damage to the eternal life of the soul.

The Torah davka put the din of vechai bahem here to teach us that sometimes, vechai bahem means that we have to give up our lives.