Acharei Mot - Passion and Inspiration

You shall observe My statutes and My ordinances, which a man shall do and live by them.

וּשְׁמַרְתֶּם אֶת חֻקֹּתַי וְאֶת מִשְׁפָּטַי אֲשֶׁר יַעֲשֶׂה אֹתָם הָאָדָם וָחַי בָּהֶם

Vayikra 18:5

In Mesechet Yoma (85B), there is an exploration amongst various Tannahs into what is the source of the reasoning that Pikuach Nefesh (saving a life) takes precedence over observing Shabbat.

R. Ishmael, R. Akiba and R. Eleazar b. Azariah were once on a journey, with Levi ha-Saddar 20
and R. Ishmael son of R. Eleazar b. Azariah following them. Then this question was asked of them:
Whence do we know that in the case of danger to human life that the laws of the Sabbath are suspended?
— R. Ishmael answered and said: If a thief be found breaking in.21 Now if in the case of this one it is doubtful whether he has come to take money or life; and although the shedding of blood pollutes the
land, so that the Shechinah departs from Israel, yet it is lawful to save oneself at the cost of his life how much more may one suspend the laws of the Sabbath to save human life!
— R. Akiba answered and said: If a man come presumptuously upon his neighbour etc. thou shalt take him from My altar, that he may die.22 I.e., only off the altar, but not down from the altar.23 And in connection therewith
— Rabbah b. Bar Hana said in the name of R. Johanan: That was taught only when one's life is to be
forfeited, but to save life1 one may take one down even from the altar. Now if in the case of this one, where it is doubtful whether there is any substance in his words or not, yet [he interrupts] the service in the Temple [which is important enough to] suspend the Sabbath, how much more should the saving of human life suspend the Sabbath laws!
— R. Eleazar answered and said: If circumcision, which attaches to one only of the two hundred and forty-eight members of the human body, suspends the Sabbath,2 how much more shall [the saving of] the whole body suspend the Sabbath!
— R. Jose son of R. Judah said: Only ye shall keep My Sabbaths,’3 one might assume under all circumstances, therefore the text reads: ‘Only’ viz, allowing for exceptions.4 R. Jonathan b. Joseph said: For it is holy unto you;5 I.e., it [the Sabbath] is committed to your hands, not you to its hands.

The Amorah, Rav Yehudah said in the name of Samuel: If I had been there, I should have told them something better than what they said: "He shall live by them,"(Vayikra 18:5) but he shall not die because of them.

So we see from here that the verse "live by them" comes to tell us that in face of transgressing a mitzvah, it is preferred to transgress and live (except in 3 cases: spilling blood, illicit relations, and idolatry).

Eternal Life
On the other hand, the translation of Onkeles brings another perspective to this verse. Targum Onkleles describes this verse as "chayei alma" - eternal life, which refers to The World to Come. Furthermore, even if there is any doubt about the interpretation that Targum Onkeles brings, Rashi states the same position with straightforward, concrete terms.

"and live by them": in the World-To-Come. For if you say [that the verse refers to living] in this world, does [everyone] not eventually die? 

Torath Kohanim 18:134

Thus we face a conflict. On the one hand "live by them" means to live in this world, and on the other hand this expression refers to another life, life in the world to come. Which is it?

Passion for Life
The Slonimer Rebbe brings in The Netivot Shalom an insight that clarifies this contradiction, saying that both of these approaches are valid and word of Hashem.

He brings a teaching from the Karliner Rebbe, saying when one reached the world to come an announcement went out that he kept Shabbat diligently according to all the details of the statutes of Shabbat. Yet just as this one kept Shabbat perfectly but without enthusiasm for Oneg Shabbat, so also his experience in the world to come is dry and didactic without Oneg.

Says The Slonimer, we learn from this that how we perform the mitzvot impact the type of world to come that we create for ourselves. Where we perform mitzvot with passion, excitement and enthusiasm so also is that feeling carried over to our world to come. Likewise, explains The Slonimer, transgressions impact life on the other side, as he explains that the fires of Gehenom are lit by the transgressions of this world.

So we see we can bring these two seemingly contradictory points of view together on the meaning of the verse "live by them." It is both about this world and the next, for just how we approach the mitzvot in this world directly impact and shape how we will experience our place in the world to come.