“Men Gain Eternal Life through the Oath and Covenant of the Priesthood”
Doctrine and Covenants 84:33–44
33 For whoso is faithful unto the obtaining these two priesthoods of which I have spoken, and the magnifying their calling, are sanctified by the Spirit unto the renewing of their bodies.
34 They become the sons of Moses and of Aaron and the seed of Abraham, and the church and kingdom, and the elect of God.
35 And also all they who receive this priesthood receive me, saith the Lord;
36 For he that receiveth my servants receiveth me;
37 And he that receiveth me receiveth my Father;
38 And he that receiveth my Father receiveth my Father’s kingdom; therefore all that my Father hath shall be given unto him.
39 And this is according to the oath and covenant which belongeth to the priesthood.
40 Therefore, all those who receive the priesthood, receive this oath and covenant of my Father, which he cannot break, neither can it be moved.
41 But whoso breaketh this covenant after he hath received it, and altogether turneth therefrom, shall not have forgiveness of sins in this world nor in the world to come.
42 And wo unto all those who come not unto this priesthood which ye have received, which I now confirm upon you who are present this day, by mine own voice out of the heavens; and even I have given the heavenly hosts and mine angels charge concerning you.
43 And I now give unto you a commandment to beware concerning yourselves, to give diligent heed to the words of eternal life.
44 For you shall live by every word that proceedeth forth from the mouth of God.
President Joseph Fielding Smith wrote:
“Every man who is ordained to an office in the Melchizedek Priesthood should realize fully just what that ordination means. He receives the priesthood with an oath and covenant that he will magnify his calling and be faithful therein [see D&C 84:33]. This oath and covenant when received in the fulness will entitle a man to become a member of the Church of the Firstborn, and the elect of God. He receives the fulness of the Father’s kingdom and is entitled, if faithful to the end, to all that the Father hath [see D&C 84:34–38]. This oath and covenant cannot be treated lightly, and if broken and altogether turned from, the man thus guilty has no forgiveness, that is to say, he will not again have these privileges granted to him which bring exaltation, or all that the Father hath [see D&C 84:41, 38]. He will stand aside without these blessings, but does not become a son of perdition because of this serious offense. The oath and covenant belonging to the priesthood, pertains to the Melchizedek Priesthood and not to the Aaronic, although it is also a serious matter to turn away or violate that blessing [see History of the Church, 5:555].”
(Church History and Modern Revelation, 2 vols. , 1:339.)