RSRH Zatzal explains that the idea of “Nazir” is “raising” a person who is striving to be alone with Hashem, and others have to keep away from him. His closeness to Hashem makes him higher and aloof compared to others. The same with the: ציץ Tzitz of the Cohen Gadol, which is called נֵזֶר הַקֹּדֶשִׁכטִו “Nezer HaKodesh” (similar to Nazir). The Shulchan, Aron, and Mizbeach all have a: זֵר crown. We can suggest that they are all messages, that: כֶתֶר כִהוּנִה, כֶתֶר תּוֹרִה, וִכֶתֶר מַלכוּת the crown of Torah, the crown of Kehuna, and the crown of Malchus, are all Maalos which are exclusive to those who were Zoche to them.
A Cohen has to know that he is special, and nobody else can be like him. Look what happened to Uziyah Melech Yehuda when he wanted to do Avoda in the Bais Hamikdash; he became a Metzora and he had to spend the rest of his life outside Yerushalayim. And this is despite his being a big Tzaddik! And the same the other way around, i.e., a Cohen cannot be a Melech. Look how the Chashmonaim (i.e., Cohanim) were all killed out when they took over the Malchus, even though they were such Tzaddikim, that if not for them, the entire Torah would have been forgotten from Klal Yisroel! (Ramban).
