In Matthew 16:18, Jesus said, "I tell you that you are Peter, and on this rock I will build my church, and the gates of Hades will not overcome it." The disciple to whom Jesus addressed this statement was named Simon. But Jesus changed his name to Peter (Greek, Petros), which means "rock." The Reformers claimed that because the usual Greek word for rock, petra, is slightly different from Petros, Jesus must have been contrasting Peter with the rock. They claimed that it was really Peter's statement that Jesus was the Christ that was the "rock" upon which Jesus would build His Church.
But Jesus spoke to His disciples in Aramaic, not Greek, and in Aramaic, the same word, Kepha, would have appeared in both places in the sentence. Therefore, most modern Protestant scholars have abandoned the Reformers' argument and they now agree with the Catholic Church that Peter was the rock to which Jesus referred. For example, Protestant scholar Oscar Cullman, writing in the Theological Dictionary of the New Testament, writes,
The Aramaic original of the saying enables us to assert with confidence the formal and material identity between p tra [petra] and P tros; P tros = p tra. . . . The idea of the Reformers that He is referring to the faith of Peter is quite inconceivable . . . for there is no reference here to the faith of Peter. Rather, the parallelism of "thou art Rock" and "on this rock I will build" shows that the second rock can only be the same as the first . It is thus evident that Jesus is referring to Peter, to whom he has given the name Rock. . . . To this extent Roman Catholic exegesis is right and all Protestant attempts to evade this interpretation are to be rejected.
Also, David Hill, a Presbyterian minister at the University of Sheffield wrote,
It is on Peter himself, the confessor of his Messiahship, that Jesus will build the Church. . . . Attempts to interpret the 'rock' as something other than Peter in person (e.g. his faith, the truth revealed to him) are due to Protestant bias, and introduce to the statement a degree of subtlety which is highly unlikely.