Once one has been faithful in the Aaronic and the Melchizedek Priesthood, which one was ordained to, one can then "also" receive the fulness of the priesthood, which one receives directly from God by His own voice and not by any ordination of man or men. One receives this "priest" HOOD (brotherHOOD, neighborHOOD, etc) by receiving the Lord Himself. It is an association with God and angels. One partakes in association with such High Priests after the order of the Son of God. It is the Father who gives the oath that one is a partaker of His glory, power, etc. God declares it. He alone confirms this priesthood by His own voice. And what is this priesthood and power associated with it?D&C 84:33 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.
Though Enoch was first ordained to the priesthood by Adam at age 25 (D&C 107:48), he later received the fullness by God, Himself, as we read above in JST Genesis 14. The same thing with Moses, who was first ordained by Jethro (D&C 84:6), yet Moses received the fullness by God, Himself, just like Enoch did and had power to bring forth water from a rock and part the Red Sea. There are other examples. Thus by the "oath and covenant" that God personally makes to each who comes unto this priesthood as we read above in D&C 84 after previously being ordained by man, does one obtain that fullness from God directly, which power in the priesthood enables one to turn rivers from their courses, set at defiance the armies of nations, etc. unto the redeeming of Zion (bringing a Zion people back into God's presence by the parting of the veil). It is one thing to be ordained to the Aaronic priesthood and the Melchizedek priesthood as many men are in the church to administer saving ordinances. It is entirely another to be ordained personally by the calling of Jehovah's own voice, by an oath, which He swears and cannot break, enabling those who now associate as fellow "high priests" to have power over the elements. When Moses was taken, the Melchizedek Priesthood was taken. When Joseph Smith was taken, a portion of the Melchizedek Priesthood remained. It is up to each to come unto the priesthood offered by God alone by His own voice through that oath and covenant, which He cannot break.JST Genesis 14:27 And thus, having been approved of God, he was ordained an high priest after the order of the covenant which God made with Enoch,
28 It being after the order of the Son of God; which order came, not by man, nor the will of man; neither by father nor mother; neither by beginning of days nor end of years; but of God;
29 And it was delivered unto men by the calling of his own voice, according to his own will, unto as many as believed on his name.
30 For God having sworn unto Enoch and unto his seed with an oath by himself; that every one being ordained after this order and calling should have power, by faith, to break mountains, to divide the seas, to dry up waters, to turn them out of their course;
31 To put at defiance the armies of nations, to divide the earth, to break every band, to stand in the presence of God; to do all things according to his will, according to his command, subdue principalities and powers; and this by the will of the Son of God which was from before the foundation of the world.
32 And men having this faith, coming up unto this order of God, were translated and taken up into heaven...