LEV67 We must not do anything that might create animosity. The Talmud comments on the words, "When he is anointed" that only one High Priest at a time is anointed, not two. Why? Rabbi Yohanan explains that this is to prevent animosity. (Yerushalmi Yoma 1:1). The essence of the High Priest is the attribute of peace. Aharon, the first High Priest, was renowned as a lover and pursuer of peace. The High Priest must unite the entire nation. If there would be animosity in this high position, it would be a distortion and mockery of the concept of the High Priest. Therefore, nothing maybe done to create such animosity. (Yalkut Yehuda, on this verse).