The Quorum of the Twelve Apostles Is a Traveling Council That Holds the Keys to Advance the Lord’s Kingdom across the World under the Direction of the President of the Church
Doctrine and Covenants 124:127–128
127 I give unto you my servant Brigham Young to be a president over the Twelve traveling council;
128 Which Twelve hold the keys to open up the authority of my kingdom upon the four corners of the earth, and after that to send my word to every creature.
President Gordon B. Hinckley said:
“On January 19, 1841, the Lord said through the Prophet Joseph: ‘I give unto you my servant Brigham Young to be a president over the Twelve traveling council; which Twelve hold the keys to open up the authority of my kingdom upon the four corners of the earth, and after that to send my word to every creature’ (D&C 124:127–128). . . . It is abundantly clear that the Lord placed the Council of the Twelve, with Brigham Young as its president, next to the Prophet Joseph Smith and gave unto them the keys and the authority to advance the Church under the direction of the Prophet while he was alive, and to govern after his death.”
(“The Joseph Smith III Document and the Keys of the Kingdom,” Ensign, May 1981, 20–21.)