G-d instructed Moses to tell the Jewish people, "Of the first of your dough, donate a loaf to a priest."
Bamidbar 15:20
The Torah grants the privileges and responsibilities of the priests only to the descendants of Aaron. To be sure, all Jews are of equal inherent value and equally deserve our love and respect. However, when dealing with the question of who can be a religious practitioner or authority--we must realize that G-d has determined who can and who cannot assume these titles.
Just as priests can only be descendants of Aaron, rabbis and teachers, too, can only be individuals who have attained the necessary levels of knowledge, who are truly G-d fearing, who observe all the dictates of the Torah, and who have absorbed the traditions transmitted through the generations.
Just as we require strict qualifications for those entrusted with guiding and facilitating our external religious lives, we should equally require strict qualifications for those inner voices that purport to tell us how to behave. We should constantly question our inner voices, in order to be sure that we are being guided only by pure and positive motives.
From Kehot's Daily Wisdom