Wherefore it came to pass that my father, Lehi, as he went forth prayed unto the Lord, yea, even with all his heart, in behalf of his people.
And it came to pass as he prayed unto the Lord, there came a pillar of fire and dwelt upon a rock before him; and he saw and heard much.
1 Nephi 1:5-6
God forbid that I should sin against the Lord in ceasing to pray for you.
1 Samuel 12:23
Likewise, we as the Lord's covenant people are commanded to sustain the prophets through our prayers:
And if ye desire the glories of the kingdom, appoint ye my servant Joseph Smith, Jun., and uphold him before me by the prayer of faith.
Sometimes we talk about this entirely of terms of duty, but it is more than that. It is a principle of power by which the Lord decides what revelation to give the Church:
Unto them [the church]is his [the Prophet's] calling, that all things might be revealed unto them, whatsoever I will, according to their faith.
Without our prayers and faith, the Prophet could know all the mysteries of eternity, and he would never be inspired to reveal them to us. And without his prayers for us, the Prophet would not be the Prophet. That is the pattern in the scriptures: the prophets pray for the people, and the people pray for the prophets, as well as for themselves.