Paul rebuked Peter because of the danger of salvation for the faithful, and did not allow the latter’s sin to pass, since it was scandalous, though small. He thereby taught others that they should act magnanimously by rebuking the crimes of their prelates when these scandalise the Church and by their bad example lead others toward damnation. The princes of the Church and the princes of the world are obliged to do the same, when the pope scandalizes the Church, once he has been admonished in private and not come to his senses. For it is likely that he will be cowed [verebitur] when princes rebuke him publicly, even if he doesn’t care about the salvation of his subjects. And so even if he himself does not become good, at least he will not continue to scandalise others.

Indeed, those who can help have a much greater duty to do this than to save someone who is being led to bodily death. For they must set themselves ‘up as a wall for the house of Israel’. ‘Seeing their brothers in need and shutting up, in effect, the bowels of their mercy from them, how do they have the charity of God?’ [Commentary on the Summa Theologiae, 2a 2ae 33, 4].