“The Keys of the Kingdom of Heaven”

Matthew 16:18–19

18 And I say also unto thee, That thou art Peter, and upon this rock I will build my church; and the gates of hell shall not prevail against it.
19 And I will give unto thee the keys of the kingdom of heaven: and whatsoever thou shalt bind on earth shall be bound in heaven: and whatsoever thou shalt loose on earth shall be loosed in heaven.

Elder Bruce R. McConkie wrote:

“‘Keys are the right of presidency, the directing, controlling, governing power. The keys of the kingdom are the power, right, and authority to preside over the kingdom of God on earth (which is the Church) and to direct all of its affairs’ [Bruce R. McConkie, Mormon Doctrine, 2nd ed. (1966), 411]. These keys include the sealing power, that is, the power to bind and seal on earth, in the Lord’s name and by His authorization, and to have the act ratified in heaven. Thus if Peter performed a baptism by the authority of the sealing power here promised him, that ordinance would be of full force and validity when the person for whom it was performed went into the eternal worlds, and it would then admit him to the celestial heaven. Again, if Peter used these sealing keys to perform a marriage, then those so united in eternal marriage would continue as husband and wife forever. When they attained their future heaven, they would find themselves bound together in the family unit the same as they were on earth [see Bruce R. McConkie, Mormon Doctrine, 2nd ed. (1966), 683–84].”

(Doctrinal New Testament Commentary, 3 vols. [1965–73], 1:389–90.)