D&C 124:104; New Witness for the Articles of Faith, McConkie, pp. 426-427
“Joseph was told that the seer of the latter days would also have a spokesman appointed for him. Although he, himself, would have the responsibility of bringing forth the writings of Joseph’s descendants (The Book of Mormon), the spokesman would have the responsibility of going forth to declare it. This turned out to be Oliver Cowdery whom the Lord designated as ‘The first preacher of this church unto the church, and before the world, yea, before the Gentiles; yea, and thus saith the Lord God, lo! to the Jew also’ (D&C 21:12). Later, the Lord specifically said that Oliver Cowdery had a calling ‘even as Aaron (the spokesman of Moses), to declare faithfully the commandments and the revelations, with power and authority unto the church’ (D&C 28:3). After Oliver Cowdery fell, Sidney Ridgon was designated the ‘spokesman’ (D&C 100:89).” (Cleon Skousen, Treasures of the Book of Mormon,1:1204)
“God afterwards revealed that this man, [Sidney Rigdon] was to be a spokesman, and he became the spokesman to this people and to the world for the prophet Joseph. Those who knew Sidney Rigdon, know how wonderfully God inspired him, and with what wonderful eloquence he declared the word of God to the people. He was a mighty man in the hands of God, as a spokesman, as long as the prophet lived, or up to a short time before his death. Thus you see that even this … was predicted about 1,700 years before the birth of the Savior, and was quoted by Lehi 600 years before the same event, and about 2,400 years before its fulfillment, and was translated by the power of God through his servant Joseph, as was predicted… .” (George Q. Cannon, Journal of Discourses 25:126)