The Torah's response to death reminds us of the limit to human understanding.
One of the most basic, unquestioned, and unfounded axioms of modern man is the belief in the unlimited human capacity for understanding our world. The mysteries of the universe are all temporary, just waiting for the person who will crack their code, who will discover the equation or formulate the theory that will provide us with the explanation. This belief is an integral component of the modern belief in Progress. To suggest that a natural phenomenon is beyond human understanding, that it can't be measured or tested or evaluated, is modern heresy.
But as much as human history can be rallied to prove that humanity progresses, it provides even more consistent and compelling evidence that human understanding is limited. There is, I submit, no surer, more well-founded truth statement that can be made than that "our understanding is flawed." I'm not sure it's really possible to know anything else for certain. After all, perhaps this is all a dream. Perhaps I'm a brain floating in a jar. One can be skeptical of all statements, except for this one: that my understanding of the world is lacking. The entire history of scientific progress attests to it; it's shortsighted to think that the scientific truths we are most sure of won't seem quaint, primitive, and silly in 50 or 100 years.
The limits of human understanding are proven by another demonstrable phenomenon we simultaneously ignore and obsess about- death. In a sense, human progress is a valiant, but futile, attempt to defeat death, for death deals a fatal blow to the illusion of limitless human capacity.
This is precisely the message that the Torah's ritual response to death carries. The most perplexing element of the ritual of the red heifer is its paradoxical effect, defiling the pure while it purifies the defiled. The dichotomy of pure-impure, tahor-tameh, is the major organizing principle of religious life in the desert. The Torah's response to death renders the dichotomy absurd, reminding us that ultimate meaning belongs only the Ultimate. Our own understandings of the world, even through the categories God gives us, will always be limited and lacking.