As Tod Linafelt says (The Hebrew Bible as Literature, p. 9), we tend to “get bogged down in Leviticus”. But there really is a structure to ספר ויקרא. The beginning is the story of the inauguration of the משכן and the concretization of ה׳'s forgiveness of the sin of the עגל הזהב; then from the second half of שמיני through פרשת אמור are the laws of טומאה and קדושה, the “mission” of בני ישראל (ואתם תהיו לי ממלכת כהנים וגוי קדוש) ; which leads to the restatement of ברית הר סיני in פרשת בהר־בחוקותי. Then בני ישראל are ready to start their journey into the promised land in ספר במדבר.
I finessed over the phrase “the laws of טומאה and קדושה” but they are really two separate concepts, and are two different parts of the ספר. שמיני through מצורע deal with טומאה and טהרה. Even the laws of kosher animals are presented in terms of טומאה and טהרה, as opposed to the laws in ספר דברים, which are presented in terms of forbidden and permitted foods. אחרי מות through אמור deal with קדוש and חול. As Rav Moshe Lichtenstein says:
קודשה and טהרה represent two orthogonal spiritual axes. One can be קודש and טהור; that’s our description of the angels in שחרית: וְכֻלָּם פּותְחִים אֶת פִּיהֶם בִּקְדֻשָּׁה וּבְטָהֳרָה. One can be חול and טהור; that’s our normal state of living. One can be חול and טמא; that’s what happens after we contact something טמא. The unexpected state is קודש and טמא, that tells us that the two concepts are independent. The burial society is called the חברא קדישא for exactly that reason.
To summarize: the default state of creation is טהור but חול. קדושה is man-made, artificial:
Rav Aharon makes the point more strongly. Note that he uses the term טומאה to refer to “anti-קדושה”, the forces of black magic and חלול השם, which is different from the way we are using the term here.
(שבת is the exception to this rule; ויברך אלקים את יום השביעי, ויקדש אתו. ואכמ״ל)
טומאה is different. It is not created by our actions. טומאה comes from our contact with the reality of death.
And what is striking about טומאה is, contrary to our intuition, there is nothing morally wrong with it. There is no prohibition of becoming טמא:
So why do we care? Why does the Torah spend so much time talking about it? The answer lies in the intersection of קדושה and טהרה: the בית המקדש and our עבודת ה׳.
How do we put this together? טומאה isn’t caused by death; it’s caused by our awareness of death. Being in a state טומאה forces us to be aware of our contact with the lack of life. Now, it is true that this is part of creation:
But that can’t be part of our עבודה. There’s an interesting implication in the way we say the introductory פסוקים to קידוש:
טמאה is not incompatible with קדושה; it is incompatible with מקדש, with the center of עבודה. Rav Hirsch sees this as the message of טומאה:
We don’t deny the reality of death. The laws of טומאה force us to acknowledge that we have, in some way, been in contact with the antithesis of life itself. This should not and cannot be ignored. However, this realization carries with it the idea that nothing matters. It all ends in emptiness. It’s the philosophy of nihilism.
Nowadays, we lack both a מקדש and any sense of טומאה; there is no צרעת and we have no contact with death. Ibn Ezra makes a comment that I find interesting: (אבן עזרא, שמות לד:כט) ואין אדם שלא ראה פני המת, ולא יירא מגשת אליו. That’s clearly no longer true. So the laws of טומאה and טהרה seem meaningless to us. But we still need that טהרה—the absence of טומאה, and the sense that there is a purpose in existence—in our עבודה today.