JOEL - Here is the scripture you refer to in its entire context:

Matthew 16:13 - 19
13 ¶ When Jesus came into the coasts of Caesarea Philippi, he asked his disciples, saying, Whom do men say that I the Son of man am?
14 And they said, Some [say that thou art] John the Baptist: some, Elias; and others, Jeremias, or one of the prophets.
15 He saith unto them, But whom say ye that I am?
16. And Simon Peter answered and said, Thou art the Christ, the Son of the living God.
17. And Jesus answered and said unto him, Blessed art thou, Simon Barjona: for flesh and blood hath not revealed [it] unto thee, but my Father which is in heaven.
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.

In verse 16 Peter proclaims that "Jesus is the Christ, the son of the living God". In verse 17 Jesus then explains to Peter that it was by revelation from God that he was able to recognize this. Then in verse 18 Jesus tells him that it is upon this rock(revelation) that He will build His church. He then goes on to say that He will give him "keys" so that whatever he binds on earth shall be bound in heaven.
The rock is revelation from God, which is exactly what was used through the prophet Joseph Smith and others to build and maintain The Church of Jesus Christ of Latter-day Saints, just as Jesus said He would do. And we have also obtained those "keys" He talked about when the priesthood of God was restored through the prophet Joseph Smith, who received it directly from Peter, James, and John.(JSH 1:72)