HOW PERNICIOUS, how grave the plague of vainglory! Such great justice, such manifold virtues, such depth of faith and devotion—which can change nature itself and the laws of the whole world—by one act of vanity perish. All one’s virtuous acts are consigned to oblivion, being as if they never were, and one immediately incurs the wrath of the Lord—unless, by the very same steps of humility, one ascends again to the summit lost.
St. John Cassian, The Institutes, XI, 10.