Pope Saint Gregory VII:
That the Roman church has never erred; nor will it err to all eternity, the Scripture bearing witness.
The Roman Pontiff, if he has been canonically ordained, is undoubtedly made a saint by the merits of St. Peter, St. Ennodius Bishop of Pavia bearing witness, and many holy fathers agreeing with him. As it is contained in the decrees of Pope St. Symmachus.
He himself may be judged by no one.
Pope Innocent III:
Saint Catherine of Siena:
The Lord clearly intimates that Peter's successors will never at any time deviate from the Catholic faith, but will instead recall the others and strengthen the hesitant.Saint Thomas Aquinas:
The administration of this kingdom, therefore, is entrusted not to earthly kings, but to priests, so that spiritual and earthly things may be kept distinct; and in particular to the Supreme Priest, the successor of Peter, the Vicar of Christ, the Roman Pontiff, to whom all the kings of the Christian people should be subject, as if to the Lord Jesus Christ Himself.Pope Boniface VIII:
But if the highest power of all err, it can be judged only by God, and not by man.
Furthermore, we declare, we proclaim, we define that it is absolutely necessary for salvation that every human creature be subject to the Roman Pontiff.
Saint Catherine of Siena:
For divine obedience never prevents us from obedience to the Holy Father: nay, the more perfect the one, the more perfect is the other. And we ought always to be subject to his commands and obedient unto death. However indiscreet obedience to him might seem, and however it should deprive us of mental peace and consolation, we ought to obey; and I consider that to do the opposite is a great imperfection, and deceit of the devil.Pope Pius II:
Do you not know, you miserable man, that only divine authority binds the Roman Bishop? The Pope is only subject to Holy Scripture, revealed by the hand of God, and he is not bound by decrees of men. ”But we say that the pope is subject to reason, and the power of the Church is given for edification and not for destruction.” But even if you believe the Bishop of Rome to be in error, that does not give you the right to judge him, for only God can judge the Pope. No mortal man may accuse him of faults. Oh, how wrong is the opinion of many men: though they do not allow a king’s subjects to have any say against the king, they would allow it in the case of the pope even if God has given him power over all mortal men. Those stupid men are unconcerned that the Holy Apostolic Church has, from Saint Peter to this day, never been heard to teach anything that is contrary to orthodox faith. This privilege it has received from the Lord that it shall never succumb to wrong teachings for the gates of hell shall not prevail against it. Let this suffice concerning your praise of the Apostolic See.The Fifth Lateran Council:
For it is clearly established that only the contemporary Roman pontiff, as holding authority over all councils, has the full right and power to summon, transfer and dissolve councils. This we know not only from the witness of holy scripture, the statements of holy fathers and our predecessors as Roman pontiffs, and the decisions of the sacred canons, but also from the declarations of the same councils.
Moreover, since subjection to the Roman pontiff is necessary for salvation for all Christ's faithful, as we are taught by the testimony of both sacred scripture and the holy fathers, and as is declared by the constitution of pope Boniface VIII of happy memory, also our predecessor, which begins Unam sanctam, we therefore, with the approval of the present sacred council, for the salvation of the souls of the same faithful, for the supreme authority of the Roman pontiff and of this holy see, and for the unity and power of the church, his spouse, renew and give our approval to that constitution, but without prejudice to the declaration of pope Clement V of holy memory, which begins Meruit.