“The Lord says to Peter: ‘I say to you,’ he says, ‘that you are Peter, and upon this rock I will build my Church, and the gates of hell will not overcome it. … ’ [Matt. 16:18]
. On him [Peter] he builds the Church, and to him he gives the command to feed the sheep [John 21:17], and although he assigns a like power to all the apostles, yet he founded a single chair [cathedra], and he established by his own authority a source and an intrinsic reason for that unity. . . . If someone [today] does not hold fast to this unity of Peter, can he imagine that he still holds the faith? If he [should] desert the chair of Peter upon whom the Church was built, can he still be confident that he is in the Church?” (The Unity of the Catholic Church 4; first edition [A.D. 251]).
“Cornelius was made bishop by the decision of God and of his Christ, by the testimony of almost all the clergy, by the applause of the people then present, by the college of venerable priests and good men, at a time when no one had been made [bishop] before him—when the place of [Pope] Fabian, which is the place of Peter, the dignity of the sacerdotal chair, was vacant. Since it has been occupied both at the will of God and with the ratified consent of all of us, whoever now wishes to become bishop must do so outside. For he cannot have ecclesiastical rank who does not hold to the unity of the Church” (Letters 55:[52]):8 [A.D. 253]).
“With a false bishop appointed for themselves by heretics, they dare even to set sail and carry letters from schismatics and blasphemers to the chair of Peter and to the principal church [at Rome], in which sacerdotal unity has its source” (ibid., 59:14).