In conferring the Aaronic Priesthood upon Joseph Smith and Oliver Cowdery (D&C 13), John the Baptist prophesied the priesthood would never again be taken from the earth "until the sons of Levi do offer again an offering unto the Lord in righteousness."
The sons of Levi historically were worthy male members of the Levitical tribe chosen by Moses to administer in the ordinances of the priesthood under the presidency of Aaron and his sons. Joseph Smith taught that the future "offering unto the Lord in righteousness," to which John referred, is literally a sacrificial offering as was performed anciently."The offering of sacrifice has ever been connected and forms a part of the duties of the Priesthood," he wrote in 1840. "It began with the Priesthood, and will be continued until after the coming of Christ, from generation to generation. . . .
"These sacrifices, as well as every ordinance belonging to the Priesthood, will, when the Temple of the Lord shall be built, and the sons of Levi be purified, be fully restored and attended to in all their powers, ramifications, and blessings. This ever did and ever will exist when the powers of the Melchizedek Priesthood are sufficiently manifest; else how can the restitution of all things spoken of by the holy Prophets be brought to pass? It is not to be understood that the law of Moses will be established again with all its rites and variety of ceremonies; this has never been spoken of by the Prophets; but those things which existed prior to Moses' day, namely sacrifice, will be continued.
"It may be asked by some, what necessity for sacrifice, since the Great Sacrifice was offered? In answer to which, if repentance, baptism, and faith existed prior to the days of Christ, what necessity for them since that time? The Priesthood has descended in a regular line from father to son, through their succeeding generations. (History of the Church 4:211-212.)
President Joseph Fielding Smith explained: "The sacrifice of animals will be done to complete the restoration when the temple spoken of is built; at the beginning of the millennium, or in the restoration, blood sacrifices will be performed long enough to complete the fulness of the restoration in this dispensation. Afterwards, sacrifice will be of some other character." (Doctrines of Salvation, 3:94.)