“Now I say to you that you are Peter (which means ‘rock’), and upon this rock I will build my church, and all the powers of hell will not conquer it.”
—Matthew 16:18, New Living Translation
Jesus spoke Aramaic, as we can see in the same Gospel Jesus speaking in Aramaic, ‘Eli, Eli, lama sabachthani?’ (Matthew 27:46). So Jesus must have spoken in Aramaic when he delivered the words in Matthew 16:18. The word he called Peter was “Kepha”, the Gospel of John records this (Cephas). In Aramaic the word “Kepha” means “rock”, so Christ said to Peter, “You are Kepha, and this Kepha I will build my Church”. And from a translation of Aramaic Peshitta,
“who is in heaven my Father but my church I will build Keepa this and on Keepa are that you I will give to you will subdue it not of Sheol”
—Mattai 16:18, Peshitta Aramaic/English Interlinear New Testament (The Preaching of Mattai)
And from reading John 1:42, we see that it was in Aramaic, Peter’s name was a translation of the original Aramaic.
Hebrew: you Kefa and upon this kefa
Old Syriac (C): Anath-her Kipha, v’all hode kipha
“You are Simon, son of John. You will be called Cephas” (which means “Rock”).
—Holman Standard Christian Bible
“You are Simon, son of John: you shall be called Cephas” –that is to say, Peter (or ‘Rock’)”
—Weymouth New Testament
”Thou art Simon, the son of Jonas, thou shalt be called Cephas,’ (which is interpreted, A rock.)‘
—Young’s Literal Translation
As one Protestant commented on this (John 1:42), “The stone, or rock, is a symbol of firmness and steadiness of character – a trait in Peter’s character after the ascension of Jesus that was very remarkable.” (Notes on the Bible by Albert Barnes ). Peter (Cepha-Rock) was called that by Christ, taking from the original language Christ spoke. We cannot deny that Christ called Peter Cepha. Even other verses in the Bible call Peter “Cepha” (1 Cor 9:5, 1:12, 3:22, 15:5; Gal 1:18, 2:9, 2:11). If Peter was not the “Rock”, why does Paul and Christ Himself call Peter “Kepha”?