24 Read in this light, the prophetic text leads to one conclusion: we need knowledge, we need truth, because without these we cannot stand firm, we cannot move forward. Faith without truth does not save, it does not provide a sure footing. It remains a beautiful story, the projection of our deep yearning for happiness, something capable of satisfying us to the extent that we are willing to deceive ourselves. Either that, or it is reduced to a lofty sentiment which brings consolation and cheer, yet remains prey to the vagaries of our spirit and the changing seasons, incapable of sustaining a steady journey through life. If such were faith, King Ahaz would be right not to stake his life and the security of his kingdom on a feeling. But precisely because of its intrinsic link to truth, faith is instead able to offer a new light, superior to the king’s calculations, for it sees further into the distance and takes into account the hand of God, who remains faithful to his covenant and his promises.
Source: Lumen Fidei (Vatican.va)