“And I also say to you that you are Peter (Petros), and upon this rock (petras) I will build My church; and the gates of Hades shall not overpower it” (Matt 16:18).
The Protestian agruement is the rock is Christ not Peter. In verse Matt 16:18 Peter is the masculine Petros where this rock is petras. In the following verses Christ is refered as petra, and even Peter in his letter used petra to refer to Christ:
“and all drank the same spiritual drink, for they were drinking from a spiritual rock (petras) which followed them; and the rock (petra) was Christ” (1 Cor. 10:4).
“speaking of Jesus says that he is “A stone of stumbling and a rock (petra) of offense”; for they stumble because they are disobedient to the word, and to this doom they were also appointed” (1 Pet. 2:8).
I recognize the context of Matt 16:18 is the installation of Peter as authority over the church, but I’m curious why petras was used instead of petros for rock. Perhaps to clarify the play on words otherwise missed without petras. I don’t know.
Argument taken from carm.org/catholic/peter.htm