D&C 128:24 . Who Are the Sons of Levi, and What Is Their Offering?
Historically, the sons of Levi, including the sons of Aaron and the sons of Moses (see Exodus 6:16, 18, 20 ), were the custodians of the house of God and were responsible for its ordinances (see Exodus 25–28 ; Numbers 8:24–26 ; 10:21 ). Today the Lord promises that men who are called by the Lord to “build up my Church” and who are “faithful unto the obtaining these two priesthoods of which I have spoken, and the magnifying their calling,” become the “sons of Moses and of Aaron” ( D&C 84:32–34 ; see v. 31 ). The Aaronic Priesthood is responsible for the “preparatory gospel” ( v. 26 ; see v. 27 ). In the ordinances of the Melchizedek Priesthood, including temple work, “the power of godliness is manifest” ( v. 20 ; see vv. 19–22 ). As righteous Saints serve the Lord in holy ordinances, including those of the temple, the sacrifice they offer through their service will be part of the “offering in righteousness” that the sons of Levi, including the sons of Moses and Aaron, will present to the Lord before His coming.
Never has a people had the opportunity to do so much for so many as do the Latter-day Saints. If they fail to fulfill their duty, they do so at the “peril of their own salvation” (Smith, Teachings, p. 193; see also p. 356). The dead cannot receive the ordinances that lead them to salvation unless they are performed by the living, and the living must bind themselves to their ancestral families for their own salvation. Little wonder that the Prophet Joseph Smith expressed such strong feeling for the Lord’s saving plan. All Saints should feel the same urgency.
(Doctrine and Covenants Student Manual p.319)