John Cassian

And so it is most clearly established by examples and testimonies from Scripture that the mischief of pride, although it comes later in the order of the combat, is yet earlier in origin and is the beginning of all sins and faults. Neither is it (like the other vices) simply fatal to its opposite virtue—that is, humility—but it is also at the same time destructive of all virtues. Nor does it only tempt ordinary folk and small people, but chiefly those who already stand on the heights of valor. For thus the prophet speaks of this spirit, "His food is choice." And so the blessed David, although he guarded the recesses of his heart with the utmost care, so that he dared to say to him from whom the secrets of his conscience were not hid, "Lord, my heart is not exalted, nor are my eyes lifted up; neither have I walked in great matters, nor in wonderful things above me. If I was not humble" and again, "He that is proud shall not dwell in the midst of my house." Still, because he knew how hard that watchfulness is even for those that are perfect, he did not so presume on his own efforts, but prayed to God and implored his help, that he might escape unwounded by the darts of this foe, saying, "Let not the foot of pride come to me." For he feared and dreaded falling into that which is said of the proud, namely, "God resists the proud" and "Every one that exalts his heart is unclean before the Lord."