Musar על אבות 3:13

Silence becomes sages; how much more so, fools. (Avoth 3:17): "A fence for wisdom is silence." "Silence is the universal cure." And guard your tongue like the pupil of your eye. (Mishlei 18:7): "The mouth of a fool is destruction to him, and his lips are a stumbling-block to his soul." And (Ibid. 21:23): "One who guards his mouth and his tongue guards his soul from suffering."

This was said by King Shlomo, peace be unto him: "I said of laughter, it is madness; and of merriment, what use is it?" (Ecc. 2:2). And the Sages of blessed of memory, said: "laughter and light-headedness habituate a person to illicit relations" (Avot 3:13). For even though sexual immorality is regarded as severe by every man of faith, and his heart fears approaching it, due to the vivid picture that has been imprinted in his mind of the enormity of the sin and the severe punishment it incurs, nevertheless, laughter and light-headedness draw him on little by little, advancing him nearer till the fear of sin leaves him bit by bit, degree after degree, until he reaches the sin itself and commits it.

Behold, Shlomo repeatedly exhorted many times on this in seeing the evil of laziness and the greatness of the harm resulting from it. He said "a little sleep, a little slumber, a little folding of the hands to rest. Then shall your poverty come as a traveler" (Mishlei 24:33). For behold, even though the lazy person is not doing evil actively, nevertheless he brings evil on himself through his very inactivity.

The quality of mercy identifies the descendants of Abraham our father — the seed of Israel as it is written in Deuteronomy 13:18: "And He shall show you mercy and have mercy upon you and multiply you" i.e. (God will give you the quality of mercy). Therefore, everyone should accustom himself to speak all his words with the language of petition and mercy. Also, when he prays, his prayer should be in the tone of plea and petition. And great indeed is the reward that a man will receive from his words of mercy when he speaks to the heart of the poor.

Then too, if a person is silent, others can reveal secrets to him, for inasmuch as he is not accustomed to speak much he will not reveal the secret. Moreover, it is not his habit to indulge in gossip, and concerning this it is said, "Death and life are in the power of the tongue" (Prov. 18:21), for a man can do more harm with his tongue than he can with a sword. For a man can stand here and yet betray his companion, who is a long distance from him, and cause his death (by his word), while the sword can only slay someone who is near it. Therefore man was created with two eyes, two ears, two nostrils and one mouth to say to him that he ought to speak less. Silence is fitting for the wise, and thus all the more so for fools. "A fence around wisdom is silence" (Aboth 3:13). "There is no better medicine than silence" (Megillah 18a).