Article of Faith #5, "We believe that a man must be called of God, by prophecy, and by the laying on of hands by those who are in authority, to preach the Gospel and administer the ordinances thereof."
So this goes directly in line with the way the God works. He has always done this from the beginning. We can take Aaron for example. He was called by God, set apart, and he went out and did his work. We have another example in the New Testament with the Apostles. Christ called them all together, and set apart each one and sent them off to go do their work as well, and now days we have the same thing, not only with General Authorities, but with the missionaries that you see walking around as well.