And the people of Israel said to Moses, "Behold, we perish, we are undone, we are all undone. "
Numbers 17:12

The selection of Aaron's sons as the only legitimate priesthood was a great cultural shift within Israel. Prior to this point, every family had its own priest, and anyone could act as a priest from time to time.

The narrowing of this office and role to a single lineage must have felt like God had taken away any ability to approach him, as if God had taken the Levites as his people and rejected the rest of Israel. They did not yet understand that someone from one tribe could act as a priest of YHVH for someone from another.