Dvar for Emor (Leviticus 21:1-24:23)

Rabbi Twerski explains this with a Midrash that when the Jews got the Torah, they were freed from the "Angel of Death". This means that G-d Himself conducted the process of death, and people died by the "kiss of G-d" (Moshe and Aaron pass away in this manner). This way the bodies do not induce impurity. However, after the sin of the Golden Calf, the Angel of Death's job was given back to him, and bodies once again became impure. Since Aaron was the one who still felt guilty for the sin of the Golden Calf (although he fully repented), G-d knew that mentioning the renewed laws of impurity would remind Aaron of his sin and make him feel self-conscious. It is for this reason that Aaron was excluded from the commandment. G-d went out of His way and changed a commandment of the Torah for one person's feelings. If only we were more sensitive to others' internal feelings, we would merit our own eternal purity