Nothing is better for rendering the heart penitent and the soul humble than wise solitude and complete silence. Nothing has a greater power of disturbing the state of silence, and of depriving it of God's help, than the following principal passions: presumptuousness, gluttony, talkativeness and vain cares, arrogance and the mistress of all passions - self regard. Whoever readily permits himself to acquire the habit of these passions will become, in the course of time, more and more shrouded in darkness, until finally he is completely deadened. If, however, he comes to himself and begins to practice the necessary observances with faith and zeal, he will once more obtain what he seeks, especially if he seeks it with humility. But if, through negligence, even one of the passions mentioned begins to rule in him, then the whole host of evils, with pernicious unbelief at its head, attacks and overpowers him and completely devastates his soul. The soul is then filled with diabolical confusion and turmoil and become another Babel, so that 'the last state of the man is worse than the first' (Matt. xii. 45). Then the man turns into a violent enemy and defamer of those who practice silence, always sharpening his tongue against them, like a razor or a double-edged sword.
--St. Gregory of Sinai (d. 1360), Texts on Commandments and Dogmas, 104 (Writings from the Philokalia on Prayer of the Heart, p. 59)