"Silence is a great power in our unseen warfare and a sure hope of gaining victory. Silence is much beloved of him, who does not rely on himself but trusts in God alone. It is the guardian of holy prayer and a miraculous helper in the practice of virtues; it is also a sign of spiritual wisdom. St. Isaac says: 'guarding your tongue [and ears] not only makes your mind rise to God, but also gives great hidden power to perform visible actions, done by the body. If silence is practised with knowledge, it also brings enlightenment in hidden doing' (ch. 31 in Russian edition). In another place he praises it thus: 'If you pile up on one side of the scales all the works demanded by ascetic life, and on the other side -- silence, you will find that the latter outweighs the former. Many good counsels have been given us, but if a man embraces silence, to follow them will become superfluous' (ch. 41). In yet another place he calls silence 'the mystery of the life to come; whereas words are the instruments of this world' (ch. 42). St. Barsanuphius places it above preaching the word of God, saying: 'If you are just on the very point of preaching, know that silence is more worthy of wonder and glory.' Thus, although one man 'holdeth his tongue because he hath not to answer', another 'keepeth silence, knowing his time' (Ecclesiasticus xx.6), yet another for some other reasons, 'for the sake of human glory, or out of zeal for this virtue of silence, or because he secretly communes with God in his heart and does not want the attention of this mind to be distracted from it' (St. Isaac, ch. 76). It can be said in general that a man, who keepeth silence, is found wise and of good sense (Ecclesiasticus xx.5).
I shall indicate to you the most direct and simple method to acquire the habit of silence: undertake this practice, and the practice itself will teach you how to do it, and help you. To keep up your zeal in this work, reflect as often as you can on the pernicious results of indiscriminate babbling [and listening] and on the salutary results of wise silence. When you come to taste the good fruit of silence, you will no longer need lessons about it."
Lorenzo Scupoli, Unseen Warfare. Edited by Nicodemus of the Holy Mountain and revised by Theophan the Recluse. Translated by E. Kadloubovsky and G. E. H. Palmer. Crestwood, New York: St. Vladimir's Seminary Press, 1987. Chapter 25, 146-147.