The arrangement that God and Moses had made was designed to bolster Moses’ singular authority. All spirit had to be transmitted to others via Moses (see esp. v. 25 asher alav), and the purpose of this transmission was strictly to authorize subordinates who would serve him (see esp. v. 17b: ונשאו אתך במשא העם, ולא-תשא אתה לבדך – They shall share the burden of the people with you, and you shall not bear it alone ). There was no place in this arrangement for individual spiritual voices that might speak independently of the figure of Moses and bring a diversity of opinions into the public domain. Eldad and Medad challenged not only the centralized and exclusive authority of Moses, but also, at least implicitly, the attempt to wield political control over the divine spirit.
Yes ~ very thoughtful. Reminds me of Saul/Paul appearing ‘out of nowhere,’ and outside the designated structure of the twelve (who became eleven).