For Jesus to build His Church, He needed a foundation. That foundation has to be made up of “rock” (as any 1st Century Carpenter would know).
So, He (in changing Simon’s name to Rock literally) was telling Simon that He would become the foundation of His Church (since it had to be built upon a “rock” foundation).
This was prophesized in Matthew 7 and is confirmed that The Apostles and the Prophets are the foundation of The Church (these men who are called by God are ordained by God and cease being mere men…they are no longer just made of soil, but echo Christ.
Christ was not changing Peter’s name at the time of Matthew 16. That is not Scriptural as Peter had been called by that name for quite some time.
Matthew 16:18 has been mis-interpreted for a long time by many people. In fact, Christ changed Peter’s name the very first time He met him.
John 1:42 * And he brought him to Jesus. And Jesus looking upon him, said:
Thou art Simon the son of Jona: thou shalt be called Cephas, which is interpreted Peter.*
So Peter had already had his name all during Christ’s ministry before the time of Matthew 16:18. Therefore Christ did not, at that time, change Peter’s name. He already had, long before.
Also maybe God had revealed to Peter that Jesus was the Messiah, the son of the living God,
but it had been known by many, including Peter, long before as well.
Peter’s brother Andrew had told Peter of Christ when he was following John the Baptist.
John 1:40 * And Andrew, the brother of Simon Peter, was one of the two who had heard of John, and followed him. 41) He findeth first his brother Simon, and saith to him:
We have found the Messias, which is, being interpreted, the Christ*.
That was before Peter became a disciple.
In addition, to show that Matthew 16:18 has been interpolated, Jesus had been known as the “Son of God” for quite some time before this as well.
Matt 14:33
And they that were in the boat came and adored him, saying: Indeed thou art the Son of God.
And the devils Christ cast out told everone there about Christ when they said:
Matt 8:29
And behold they cried out, saying: What have we to do with thee, Jesus Son of God? art thou come hither to torment us before the time?
Also, check Mark 1:1, Mark 5:7, Luke 1:32, Luke 1:35, Luke 4:41, Luke 8:28, John 1:18, John 1:34, John 1:49, John 3:18, John 3:36 and John 11:27.
There are many more that predates the event in Matthew 16 but why bother. It was common knowledge by then that Jesus was the Son of the Living God.
That’s why I believe this verse had been interpolated far too much by those who want to assign some primacy to Peter. It didn’t happen that way.