The protest of Numbers 16 reveals a power struggle: Precisely who is it that should serve in the position of prominence before the Lord? Though the complaint is against Moses and Aaron, the story reveals that Aaron is really the target of this rebellion, though the whole affair is a challenge to the Aaronic priesthood (note that some of the rebels are not even Levites).
Why a challenge?
The text does not say, but since the story also deals with the portion of the offerings that belong to the priests, it may well be that the antagonism was over money (the priestly portions of sacrifices), which the rebels felt should not go to just one family or tribe – or perhaps they just resented paying the minister.
Three stories follow that underscore the election of Aaron as the legitimate High Priest. First, God burns up the rebels and leaves Aaron. Second, Aaron makes successful intercession for the people of Israel before they can all be killed by a plague for grumbling against Moses and Aaron. And third, Aaron’s staff buds, blossoms and produces almonds. Aaron is God’s choice.
On the matter of election (and remember we are God’s elect), one should be reluctant to challenge any servant of the Lord. David will say of Saul: “The Lord forbid that I should lay a hand on the Lord’s anointed.” And Paul will say of Christians who criticize one another: “Who are you to judge some else’s servant? To his own master he stands or falls.”