Did G-d ever reveal why a person was declared "unclean" if he touched a dead body?
In Hebrew, the word impurity (tumah) is related to the word confusion (timtum). Any time a human experiences spiritual confusion whose origin is in the physical world there is tumah. For example, contact with the dead gives the maximum degree of tumah because it is the ultimate illusion. One sees a dead corpse, no soul, no immortality, no spiritual essence, just flesh. A persons soul feels wounded and confused, because it knows that the essence of the human is eternal, infinite and spiritual. Sleep also imparts a very minimum degree of tumah because during sleep the physical instinct takes over from the spiritual free will.
- Rabbi Samson Raphael Hirsch, Commentary on Leviticus 12 and Numbers 19