After the 250 men who challenged Moshe and Aharon are killed by the heavenly fire, Hashem instructs Moshe to have Elazar take the pans used in the test of the Ketoret and make a cover for the Mizbeach. The goal is so that others will not be “like Korach and his congregation.”
The Gemara (Sanhedrin 110a) uses this as the source that one should not be “machzik b’machloket – hold on to fights.” The Meforshim debate whether this is merely an asmachta (Rambam in Sefer Hamitzot Shoresh 8) or a full fledged mitzvah (Meiri, R. Yonah in Shaarei Teshuva 3:58-9). The Ramban in Shichichat HaLavin insists that it is a mitzvah, though he suggests that it is not a generic prohibition against machloket. Rather, as he clarifies in his comments to the Shorashim (above), the prohibition is specifically against challenging the Kehuna (see also Smak 132).
Much has been written about this Ramban, but I wonder whether it is connected to another somewhat unique position of his. In Bereshit 49:10, the pasuk asserts that “lo yasur shevet m’Yehuda.” The Meforshim debate whether this is simply a promise that the kingship will belong to the Shevet of Yehuda, or a prohibition for other tribes to take the kingship (with many variations within the meforshim). The Ramban, based on a Yerushalmi, raises the possibility that it is only prohibited for Kohanim to become kings. This explains why it was so problematic for the Chasmonaim, who were Kohaim, to take power.
I wonder if there is a connection. Both emphasize that there is a particular problem with blurring the lines when it comes to the Kohanim. No one can challenge them, and they can’t try to take leadership roles that weren’t already given to them. This is just the beginning of an idea, but if anyone has evidence from other passages in Ramban that support the notion that there is a overarching concern for maintaining the uniqueness of the Kehuna, it would be appreciated.