What the Fullness is
From time to time throughout the history of the earth, men have lived to whom God has given the fullness of the priesthood. One such man was Enoch. To him God said,
Behold my Spirit is upon you, wherefore all thy words will I justify; and the mountains shall flee before you, and the rivers shall turn from their course; and thou shalt abide in me, and I in you; therefore walk with me. (Moses 6:34)
In God's word to Enoch, we can dispel several common misconceptions about the fullness. First, God does not give his power to men with no strings attached. It is not a delegation of his power. Instead, as we see above, the qualification for this blessing is that his Spirit (his word, his light, his truth) are upon Enoch. Enoch has absorbed the words of God to such a degree that his words are like unto God's. For that reason, God is able to announce that creation will respond to Enoch as it responds to God. As God dwells in Enoch through the dispensation of his word to Enoch's soul, Enoch dwells in God through the same mechanism. Both personages are tied to each other through the word of God, which they both have absorbed into themselves and heeded to the point of it being the sole actuating force of them both.
God gives us another example of the requirement for the recipient to have sought, obtained, and absorbed the word of God into his very being in the person of Nephi, son of Helaman. He tells Nephi, "all things shall be done unto thee according to thy word, for thou shalt not ask that which is contrary to my will."1 As with Enoch, God indicates that Nephi has obtained and absorbed enough of God's word that his personality and character have come to be like Christ's. Therefore, he will not ask for that which is contrary to the nature and will of God. Even when God gives his word to someone conveying the fullness of the priesthood, there is no blank check of authority transmitted. We see this over and over again with characters to whom God gives a fullness: they still pray and ask God what to do.
O Lord, thou didst hearken unto my words when I said, Let there be a famine, that the pestilence of the sword might cease; and I know that thou wilt, even at this time, hearken unto my words, for thou saidst that: If this people repent I will spare them. (Helaman 11:14)
They are still subject to his will. Not by force, but because they choose to be. Their power is not autonomous. It is always derived from God through his word, and is always subject to his word and his law.
We may wonder how to obtain this blessing. Jesus taught us how. He said that all who consistently seek and heed his word will also attain the character of God and will be given the fullness. "If ye abide in me, and my words abide in you, ye shall ask what ye will, and it shall be done unto you."2 This pattern is further explained in D&C 84:
And I now give unto you a commandment to beware concerning yourselves, to give diligent heed to the words of eternal life. For you shall live by every word that proceedeth forth from the mouth of God. For the word of the Lord is truth, and whatsoever is truth is light, and whatsoever is light is Spirit, even the Spirit of Jesus Christ. And the Spirit giveth light to every man that cometh into the world; and the Spirit enlighteneth every man through the world, that hearkeneth to the voice of the Spirit. And every one that hearkeneth to the voice of the Spirit cometh unto God, even the Father. And the Father teacheth him of the covenant which he has renewed and confirmed upon you, which is confirmed upon you for your sakes, and not for your sakes only, but for the sake of the whole world. (D&C 84:43-48)
This description invites us to continually seek and heed the word of God, which is the voice of the Spirit, which is light and truth. All those who do this come to Christ and the Father. This is the process by which the fullness is received.