Parshas Emor

This week's parsha speaks about Kohanim and their kedusha. We learn that kohanim aren't permitted to be metama -defile- themselevs through the dead and that a baal mum cannot officiate in the bais hamikdush. Let's try to understand why this is.
R. Yonnason Eibshitz explains the reason a kohen must be "whole" is that we know that the point of mitzvos is to get closer to Hashem. Being so, every mitzva we do we get closer to hashem. Every mitzva has its own 'channel' that connects you to that closeness. (i.e. when we keep shabbos we connect to that spiritual rest, the part of Hashem that radiates rest to the world). Further more we are taught that 613 mitzvos represent 613 body parts. So when one does a mitzva the representative body part connects to hashem. Our bodies are the vessel that recieves hashems blessings - each one with connection to its representative mitzvah.
A kohen, being that they are klal Yisroels link to the one above - they're the ones that bring our avodah- the Korbonos, to Hashem. They must be whole so that they can recieve the complete spiritual wealth from hashem and transfer it to us. When the Kohanim do the avodah in the bais hmikdosh they don't just have to be physically whole but their spiritual well being must be at the highest level and thats only possible if they're completly healthy so that they get the best possible connection to Hashem. So to, they cannot defile themselves becuse that will interrupt Hashem's radience to Klall Yisroel simply becuse Hashem cannot fully rest within them.