Chrysostom thought it the confession that mattered.
3. What then saith Christ? “Thou art Simon, the son of Jonas; thou shalt be called Cephas.”
20912091 Matt. xvi. 17, 18; see John i. 42.“Thus since thou hast proclaimed my Father, I too name him that begat thee;” all but saying, “As thou art son of Jonas, even so am I of my Father.” Else it were superfluous to say, “Thou art Son of Jonas;” but since he had said, “Son of God,” to point out that He is so Son of God, as the other son of Jonas, of the same substance with Him that begat Him, therefore He added this, “And I say unto thee, Thou art Peter, and upon this rock will I build my Church;”
20922092 Matt. xvi. 18.that is,
on the faith of his confession. Hereby He signifies that many were now on the point of believing, and raises his spirit, and makes him a shepherd. “And the gates of hell
20932093 [R.V., “Hades.”]shall not prevail against it.” “And if not against it, much more not against me. So be not troubled because thou art shortly to hear that I shall be betrayed and crucified.”
http://www.ccel.org/ccel/schaff/npnf110.iii.LII.html