The Rock in my opinion is the revelation that Jesus is the Son of God....as stated above by small fish. This is confirmed throughout the NT scriptures, affirming the fact that salvation comes to us only as we recognize the true relationship and identity of Christ. Here's some examples....
Satan even tried to get Jesus to disbelieve His own identity. Think about it. Jesus is born as a pauper, with no memory of His previous existence, required to live just as we live...by faith in the word of God. The Father spoke to Jesus, "thou art MY beloved Son". And immediately Satan tries to get Jesus to doubt His own Father's testimony...even to the point of suggesting that Satan himself is the real deal, after all, he has ownership of all these kingdoms right???
Mt 4:3 And when the tempter came to him, he said, If thou be the Son of God, command that these stones be made bread.
Mt 4:6 And saith unto him, If thou be the Son of God, cast thyself down: for it is written, He shall give his angels charge concerning thee: and in their hands they shall bear thee up, lest at any time thou dash thy foot against a stone.
But the demons did know exactly who He was...
Mt 8:29 And, behold, they cried out, saying, What have we to do with thee, Jesus, thou Son of God? art thou come hither to torment us before the time?
Jesus proclaimed it....
Joh 3:18 He that believeth on him is not condemned: but he that believeth not is condemned already, because he hath not believed in the name of the only begotten Son of God.
Joh 5:25 Verily, verily, I say unto you, The hour is coming, and now is, when the dead shall hear the voice of the Son of God: and they that hear shall live.
Joh 9:35 Jesus heard that they had cast him out; and when he had found him, he said unto him, Dost thou believe on the Son of God?
36 He answered and said, Who is he, Lord, that I might believe on him?
37 And Jesus said unto him, Thou hast both seen him, and it is he that talketh with thee.
38 And he said, Lord, I believe. And he worshipped him.
The apostles preached it, making it the foremost doctrine of the early church...
Ac 8:37 And Philip said, If thou believest with all thine heart, thou mayest. And he answered and said, I believe that Jesus Christ is the Son of God.
Ac 9:20 And straightway he (Paul) preached Christ in the synagogues, that he is the Son of God.
nd the writers of the NT all united in proclaiming it...
Paul....
2Co 1:19 For the Son of God, Jesus Christ, who was preached among you by us, even by me and Silvanus and Timotheus, was not yea and nay, but in him was yea.
Ga 2:20 I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me.
Peter....
1 Peter 1:3 ¶ Blessed be the God and Father of our Lord Jesus Christ, which according to his abundant mercy hath begotten us again unto a lively hope by the resurrection of Jesus Christ from the dead,
2 Peter1:17 For he received from God the Father honour and glory, when there came such a voice to him from the excellent glory, This is my beloved Son, in whom I am well pleased.
John...
1 Joh 1:3 That which we have seen and heard declare we unto you, that ye also may have fellowship with us: and truly our fellowship is with the Father, and with his Son Jesus Christ.
1 Joh 2:22 Who is a liar but he that denieth that Jesus is the Christ? He is antichrist, that denieth the Father and the Son.
23 Whosoever denieth the Son, the same hath not the Father: (but) he that acknowledgeth the Son hath the Father also.
24 Let that therefore abide in you, which ye have heard from the beginning. If that which ye have heard from the beginning shall remain in you, ye also shall continue in the Son, and in the Father.
1Jo 4:15 Whosoever shall confess that Jesus is the Son of God, God dwelleth in him, and he in God.
1Jo 5:5 Who is he that overcometh the world, but he that believeth that Jesus is the Son of God?
1Jo 5:10 He that believeth on the Son of God hath the witness in himself: he that believeth not God hath made him a liar; because he believeth not the record that God gave of his Son.
1Jo 5:12 He that hath the Son hath life; and he that hath not the Son of God hath not life.