In the morning the LORD will show who is his, and who is holy . . . After this you can guess what happened. The men loaded up their censers and tried to offer incense before the Lord, but God caused the earth to open its mouth and swallow up Korah, Dathan, and Abiram, then he caused fire to come out of the Tabernacle and swallow up the two hundred and fifty men offering incense, showing that they were not to be priests, not the ones to offer incense, even though God had said that in one sense the whole congregation were priests. Thus, in the Old Testament God was willing to kill people that are not priests who offer incense to him. A fusion of the office of elder and priest has taken place.
Scripture takes the distinction between clergy and laity very seriously.
Both Old and New Testaments warn people against assuming an office to which they have not been ordained. For example, I direct your attention to Jude 11, a verse most people gloss over when they read the book. For they walk in the way of Cain, and abandon themselves for the sake of gain to Balaam's error, and perish in Korah's rebellion. It is therefore possible for people, even in the New Testament, to perish in Korah's rebellion by usurping the office of the priesthood. And notice that it is not only those who actually perform the priestly duties that are subject to death, but those who follow those that have usurped priestly duties.