In a sermon dated April 6, 1853, Brigham Young said:
Perhaps it may make some of you stumble, were I to ask you a question—Does a man's being a Prophet in this Church prove that he shall be the President of it? I answer, no! A man may be a Prophet, Seer, and Revelator, and it may have nothing to do with his being the President of the Church. Suffice it to say, that Joseph was the President of the Church, as long as he lived: the people chose to have it so. He always filled that responsible station, by the voice of the people. Can you find any revelation appointing him the President of the Church? The keys of the Priesthood were committed to Joseph, to build up the Kingdom of God on the earth, and were not to be taken from him in time or in eternity; but when he was called to preside over the Church, it was by the voice of the people; though he held the keys of the Priesthood, independent of their voice. (JOD 1:133)
Commenting on this, Hoyt W. Brewster wrote:
This distinction is made whenever the members of the Church sustain the General Authorities. For example, at the April 1991 general conference, the members sustained “Ezra Taft Benson as prophet, seer, and revelatory and President” of the Church, then shortly after, they sustained “the Counselors [in the First Presidency] and the twelve Apostles as prophets, seers, and revelators.” (“The Sustaining of Church Officers, Ensign, May 1991, p. 6.) Though the office of prophet and President stand independent of one another, since the days of Joseph Smith, each man called to be President and sustained by the members of The Church of Jesus Christ of Latter-day Saints has also been a prophet. IT is inconceivable that the Saints would reject as the administrative leader of the Church the man who holds the keys of priesthood authority. (Hoyt W. Brewster, Jr., Prophets, Priesthood Keys, and Succession [Salt Lake City: Deseret Book, 1991], 30)
Elsewhere (pp. 107-8), Brewster notes:
Inherent within one's ordination to the apostolic office is the right to function within any office in the Church. This includes the authority to serve as the presiding officer in the First Presidency—the President of the Church—if the one ordained becomes the senior apostle.
President Harold B. Lee observed:
The beginning of the call of one to be President of the Church actually begins when he is called, ordained, and set apart to become a member of the Quorum of the Twelve Apostles. Such a call by prophecy, or in other words, by the inspiration of the Lord to the one holding the keys of presidency, and the subsequent ordination and setting apart by the laying on of hands by that same authority, places each apostle in a priesthood quorum of twelve men holding the apostleship.
Each apostle so ordained under the hands of the President of the Church, who holds the keys of the kingdom of God in concert with all other ordained apostles, has given to him the priesthood authority necessary to hold every position in the Church, even to a position of presidency over the Church if he were called by the presiding authority and sustained by a vote of a constituent assembly of the membership of the Church. ("The Day in Which We Live," p. 28.)
In this respect, note the comments of Elder George Q. Cannon regarding Brigham Young's selection of Elder George A. Smith to serve as a counselor in the First Presidency of the Church:
President Young, when he chose brother George A. Smith to be his First Counselor, in the place of Heber C. Kimball, did not lay his hands upon his head to confer upon him any additional power or authority for the position, because brother George A. held the Apostleship in its fulness, and by virtue of that Priesthood he could act in that or in any other position in the Church. He chose other assistant Counselors; he did not set them apart, there was no necessity for it, as they already held the Apostleship. And if he had, he could only have blessed them; he could not bestow upon them any more than they already had, because they had all that he himself had, that is when he chose them from the same Quorum. (Journal of Discourses, 19:235.)
Elder Cannon went on to say that no man who has been ordained to the apostolic office needs to have hands laid on his head and be given any additional authority when called to serve in the presidency of the Church because such a man "already possesse[s] the power, authority and ordination." He noted that such settings apart would not be wrong or improper, but they must be seen as the conferring of a blessing rather than the bestowal of any authority. Such blessings "would not bestow upon him any additional authority or any more keys, presuming that he already had received the fulness of the Apostleship." (Journal of Discourses, 19:236.)
As we enter General Conference weekend and will sustain, as the new president of the Church, Russel M. Nelson, I think one should have these ideas and doctrines in mind.