"According to the GRACE of God which is GIVEN UNTO ME, as a wise MASTERBUILDER, I HAVE LAID THE FOUNDATION, and another buildeth thereon. But let every man take heed how he buildeth thereupon. For OTHER FOUNDATION can NO MAN LAY than that IS LAID, WHICH IS JESUS CHRIST."1 Cor. 3:10,11.
Do you see what Paul is saying here? He says HE is the masterbuilder and has laid the foundation of grace, given to him by God. He goes on to say that NO MAN can lay any other foundation, the foundation being JESUS CHRIST. NOT PETER. So "the Rock" of Matt. 16:18 cannot POSSIBLY be Peter. It MUST be Jesus Christ.
424 Moved by the grace of the Holy Spirit and drawn by the Father, we believe in Jesus and confess: 'You are the Christ, the Son of the living God.' On the rock of this faith confessed by St. Peter, Christ built his Church.9 "To preach. . . the unsearchable riches of Christ"