Din Avelus

The Rambam positive commandment #37 says that we learn out from the commandment to a kohan to become tamah to his relatives that there is a commandment of avelus, to mourn over one’s dead relative.  The Rambam in the beginning of the laws of Avel cites the possuk of לא אכלתי חטאת היום as the source to the law of avelus.  So, what is the source?  The Achronim explain that the source is from the commandment to a kohan to become tamah.  The possuk at the beginning of the laws of Avel is to teach us that avelus is only one day, the seven days are only Rabbinic. 

It is clear that the Rambam holds part of avelus is the aspect of becoming tameh to the relatives.

The Rambam Avel 2:6 maintains that that woman kohanot aren’t included in the mitzvah of becoming tamah to relatives.  The Raavad disagrees.  Why does the Rambam hold woman aren’t included in the mitzvah?  He holds the mitzvah is only given to one who is normally forbidden to become tamah.  The mitzvah shows us the importance of becoming tamah by appling even to those that are forbidden to become tamah; hence it only applies to kohanim, not kohanot.