If, therefore, the Greeks or others say that they are not committed to Peter and to his successors, they necessarily say that they are not of the sheep of Christ, since the Lord says that there is only one fold and one shepherd (Jn.10:16). Whoever, therefore, resists this authority, resists the command of God Himself.
Pope Boniface VIIITherefore, if the earthly power errs, it shall be judged by the spiritual power ... but if the supreme spiritual power errs it can be judged only by God, and not by man ... Therefore we declare, state, define and pronounce that it is altogether necessary to salvation for every human creature to be subject to the Roman pontiff.
Pope Boniface VIII