The Lord provided Joseph Smith with the assistance of Oliver Cowdery. As soon as the prophet and Oliver became acquainted, the Prophet knew that Oliver had been sent to him by the Lord. If Joseph was compared unto Moses, Oliver was compared to Aaron. He was given to Joseph as a spokesman that would minister with the gift of Aaron. The Lord said to Oliver, you have another gift, which is the gift of Aaron; behold, it has told you many things; Behold, there is no other power, save the power of God, that can cause this gift of Aaron to be with you. Therefore, doubt not, for it is the gift of God (DC 8:6-8). See also DC 28:3.
Later on, the role of Joseph's spokesman was filled by Sidney Rigdon. Sidney was a great orator and preacher in another church before he was converted to Mormonism. Records of early church meetings show that Sidney spoke regularly and at great length. The Lord said, it is expedient in me that you, my servant Sidney, should be a spokesman unto this people; yea, verily, I will ordain you unto this calling, even to be a spokesman unto my servant Joseph (DC 110:9).