Numbers 19

The chapter today deals with rules regarding cleanliness again, as many past chapters have. I think I've mentioned it before, but I will say again that I don't really understand the reasoning God would have had for such procedures - what would it be about touching a dead body, or being in a tent with someone when they died, or any of the other myriad of things that made one "unclean" was so problematic? Was it purely to teach the Israelites to respect the Lord their God, or was there something scientific or health-related to it? Specifically at times of war and the like I can't imagine how the cleansing rituals were maintained reliably; imagine thousands of troops all needing to be sprinkled with water on a constant basis because they were in battle daily?