Maybe that is why the priestly office was hereditary, because otherwise hardly anyone might volunteer for it.
The onus on the kohanim was not only mechanical, limited to performing routine functions. It was also spiritual.
The point is made by a Chassidic comment on a verse in the sidra, v’esh hamizbe’ach tukkad bo - “the fire of the altar shall be kept burning on it” (Lev. 6:2).
The commentator says that in Hebrew grammar bo can mean “on it”; it can also mean “in him”, in the kohen. Kohanim had be fired with enthusiasm for their task and never treat it in perfunctory fashion.
Teaching sermon technique to rabbinical students, the late Rabbi SM Lehrman used to say, “If you can’t put fire in your sermon, put your sermon in the fire.”
Every religious role requires hitlahavut, burning fervour. Rabbi and chazan must be aflame with love of God, love of Torah, love of human beings.
It cannot be approached with the proverbial public service mentality. You never clock on or clock off. It occupies all your waking hours, and the night too (your dreams and nightmares both generally have a synagogal focus). You have to believe in what you are doing.
It becomes hard when the community does not always share your passion for God and Judaism, when you are trying to arouse them to great thoughts and noble ideals and they doggedly insist on being hard-headed and unimaginative. The result is that some rabbis and chazanim burn out and some drop out.
But most echo the words of Moses to the Levites when he inducted them into sanctuary service, Ashreichem shez’chitem lih’yot shammashim laMakom - “Fortunate are you to have the privilege of being ministers to the Almighty”.