Now I order you to retain this creed for your nourishment throughout life and never to accept any alternative, not even if I myself were to change and say something contrary to what I am now teaching, not even if some angel of contradiction, changed into an angel of light, tried to lead you astray. For even if we, or an angel from heaven, should preach to you a gospel contrary to that which you have now received, let him be accursed in your sight. – St Cyril of Jerusalem
Creeping Infallibility | Jessica M. Murdoch | First Things
Any sort of “creeping infallibility” that would attach the same level of authority to every papal utterance or document must be avoided. To fail to draw appropriate distinctions—whether between binding and non-binding documents of the ordinary magisterium, or between the development and the evolution of doctrine—is to dim the light of the Petrine ministry and impoverish the faithful.