Numbers 15 - 18

The Lord taught Aaron -

"Therefore thou and thy sons with thee shall keep your priest's office...and ye shall serve: I have given your priest's office unto you as a service of gift..." (Old Testament Numbers 18:7)

The priesthood is given for the purpose of service, for -

"...every high priest taken from among men is ordained for men in things pertaining to God, that he may offer both gifts and sacrifices for sins..." (New Testament Hebrews 5:1)

"And no man taketh this honour unto himself, but he that is called of God, as was Aaron." (New Testament Hebrews 5:4)

It appears that Korah, Dathan, and Abiram and 250 renowned Israelites, wanted to take the priesthood, this "honour" unto themselves and -

"...they gathered themselves together against Moses and against Aaron, and said unto them, Ye take too much upon you, seeing all the congregation are holy, every one of them, and the LORD is among them..." (Old Testament Numbers 16:3)

Suggesting, that there are other holy men and what makes them think that they should be in charge, asking -

"...wherefore then lift ye up yourselves above the congregation of the LORD?" (Old Testament Numbers 16:3)

After all the miracles Lord and all that Moses had done, he couldn't believe it and -

"...when Moses heard it, he fell upon his face..." (Old Testament Numbers 16:4)

We see similar groups of people in the Book of Mormon that thought they were holy saying -

"...we believe that thou hast separated us from our brethren...we believe that thou hast elected us to be thy holy children; and also thou hast made it known unto us that there shall be no Christ....and thou hast elected us that we shall be saved, whilst all around us are elected to be cast by thy wrath down to hell..." (Book of Mormon Alma 31:16 - 17)

These men had already obtained the "Levitical" priesthood but not the higher authority to administer as "priests" as Aaron and his sons. You can sense Moses unbelief as he asks -

"...seek ye the priesthood also?" (Old Testament Numbers 16:10)

The prophet Joseph Smith translated these words to -

"...seek ye the high priesthood also?..." (JST Num. 16:10)

Suggesting these men were aggressive enough to want to take the honour of the Melchizedek Priesthood upon themselves as Moses. An unrighteous insurrection such as this could lead many astray so the Lord had Moses tell them -

"...Be thou and all thy company before the LORD, thou, and they, and Aaron, to morrow:
17 And take every man his censer, and put incense in them, and bring ye before the LORD every man his censer, two hundred and fifty censers; thou also, and Aaron, each of you his censer.
18 And they took every man his censer, and put fire in them, and laid incense thereon, and stood in the door of the tabernacle of the congregation with Moses and Aaron." (Old Testament Numbers 16:16 - 18)

And so the people would know of whom the Lord called, Moses tells the people -

"Hereby ye shall know that the LORD hath sent me to do all these works; for I have not done them of mine own mind.
29 If these men die the common death of all men, or if they be visited after the visitation of all men; then the LORD hath not sent me.
30 But if the LORD make a new thing, and the earth open her mouth, and swallow them up, with all that appertain unto them, and they go down quick into the pit; then ye shall understand that these men have provoked the LORD." (Old Testament Numbers 16:28 - 30)

"And as he had made an end of speaking all these words, that the ground clave asunder that was under them:
32 And the earth opened her mouth, and swallowed them up, and their houses, and all the men that appertained unto Korah, and all their goods.
33 They, and all that appertained to them, went down alive into the pit, and the earth closed upon them: and they perished from among the congregation." (Old Testament Numbers 16:31 - 33)

"And there came out a fire from the LORD, and consumed the two hundred and fifty men that offered incense." (Old Testament Numbers 16:35)

"And no man taketh this honour unto himself, but he that is called of God, as was Aaron." (New Testament Hebrews 5:4)