What is meant by the sons of Levi offering up a sacrifice?
This phrase is first found in the prophecy of Malachi (3:1-3), promising the coming Messiah who will first purify his priesthood holders in preparation of cleansing the earth.
“The Lord whom ye seek shall suddenly come to his temple, even the messenger of the covenant, whom ye delight in; behold, he shall come, saith the Lord of Hosts. But who may abide the day of his coming, and who shall stand when he appeareth? For he is like a refiner’s fire, and like fuller’s soap. And he shall sit as a refiner and purifier of silver; and he shall purify the sons of Levi, and purge them as gold and silver, that they may offer unto the Lord an offering in righteousness.”
This prophecy was so important that the Savior recited it to the Nephites (3 Nephi 24:1-3) so they would know it also. Additionally, John the Baptist referenced it when he conferred the Aaronic Priesthood on Joseph Smith and Oliver Cowdery(Joseph Smith-History 1:69, D&C 13).
“Upon you my fellow servants, in the name of Messiah, I confer the Priesthood of Aaron, which holds the keys of the ministering of angels, and of the gospel of repentance, and of baptism by immersion for the remission of sins; and this shall never be taken again from the earth until the sons of Levi do offer again an offering unto the Lord in righteousness.”
Under the Law of Moses the tribe of Levi was given the charge of keeping the tabernacle, and later, the temple. Aaron and and his sons (who were Levites) were given the keys of performing ordinances in the tabernacle and temple. In other words, no other tribe of Israel could hold the priesthood. It was a specific duty given to the Levites alone. This is why the Aaronic Priesthood is sometimes called the Levitical Priesthood.
Because the Levites alone could perform the labors of the temple, it was the “sons of Levi” that offered sacrifices on the altar in the tabernacle and temple during Old Testament times, and even during Christ‘s ministry.
D&C 124:39 suggests that some form of Mosaic sacrifice will yet be restored to temple worship. “Your memorials for your sacrifices by the sons of Levi… are ordained by the ordinance of my holy house.” Oliver Cowdery recounted the restoration of the Aaronic Priesthood slightly differently from Joseph. He recalls the priesthood being given to them specifically so the sons of Levi could perform their duties with the proper authority:
“Upon you my fellow-servants, in the name of Messiah, I confer this Priesthood and this authority, which shall remain upon earth, that the Sons of Levi may yet offer an offering unto the Lord in righteousness!”
Besides the literal Levites, there is also a spiritual lineage of the “sons of Levi” and a spiritual offering. The oath and covenant of the priesthood (D&C 84:33-40, 34) promises the faithful that they will “become the sons of Moses and Aaron”, the same Aaron (and Moses, his brother), that I mentioned earlier as a Levite. The same section (vs 31) also states that it is specifically the sons of Moses and Aaron who will offer an acceptable offering in the temple. This is later clarified in D&C 128:24, where the Malachi prophecy is again repeated.
“Behold, the great day of the Lord is at hand; and who can abide the day of his coming, and who can stand when he appeareth? For he is like a refiner’s fire, and like fuller’s soap; and he shall sit as a refiner and purifier of silver, and he shall purify the sons of Levi, and purge them as gold and silver, that they may offer unto the Lord an offering in righteousness. Let us, therefore, as a church and a people, and as Latter-day Saints, offer unto the Lord an offering in righteousness; and let us present in his holy temple, when it is finished, a book containing the records of our dead, which shall be worthy of all acceptation.”
A great blessing has been placed upon the heads of priesthood holders. They have been granted by our Lord the power to take something as mundane as record keeping and have it sanctioned for the salvation of our dead.