In regard to their respective readiness to change, the difference between the Christian and the natural idealist is obvious. The idealist is suffused with optimism concerning human nature as such. He underestimates the depth of our defects; he is unaware of the wound, incurable by human means, with which our nature is afflicted. He overlooks our impotence to erase a moral guilt or to bring about autonomously a moral regeneration of ourselves. Moreover, his infatuation with activity prevents him from understanding even the necessity of a basic renewal. He fails to sense the essential inadequacy of all natural morality, as well as the incomparable superiority of virtue supernaturally founded, let alone the full presence of such virtue — holiness.
from Transformation in Christ by Dietrich von Hildebrand, “Readiness to Change”