Joseph Fielding Smith (Church President: January 23, 1970 - July 2, 1972)

Now, brethren, I think there is one thing which we should have exceedingly clear in our minds. Neither the President of the Church, nor the First Presidency, nor the united voice of the First Presidency and the Twelve will ever lead the Saints astray or send forth counsel to the world that is contrary to the mind and will of the Lord.

An individual may fall by the wayside, or have views, or give counsel which falls short of what the Lord intends. But the voice of the First Presidency and the united voice of those others who hold with them the keys of the kingdom shall always guide the Saints and the world in those paths where the Lord wants them to be.
Joseph Fielding Smith, “Eternal Keys and the Right to Preside,” Ensign, July 1972, 87

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I desire to say that no man of himself can lead this church. It is the Church of the Lord Jesus Christ; he is at the head. The Church bears his name, has his priesthood, administers his gospel, preaches his doctrine, and does his work.

He chooses men and calls them to be instruments in his hands to accomplish his purposes, and he guides and directs them in their labors. But men are only instruments in the Lord's hands, and the honor and glory for all that his servants accomplish is and should be ascribed unto him forever. If this were the work of man, it would fail, but it is the work of the Lord, and he does not fail.
Joseph Fielding Smith, in Conference Report, April 1970, 113