Musar su Ecclesiaste 5:5

“When you make a vow to the Lord, your God, do not delay fulfilling it” (Deuteronomy 23:22). Behold there is a punishment for the delay of vows and charity, even though one pays them later. And if someone vows to give charity to the poor, he is obligated to pay it immediately. And if by way of forgetfulness, a delay of the vow happens to him, this too will surely be punished. For since he knows that forgetfulness is found with people, he should have remembered his vows and constantly put them into his heart, so that he would not forget them - like the matter that is stated (Proverbs 20:25), “It is a snare for a man to pledge a sacred gift rashly, and to give thought to his vows only after they have been made.” Therefore, his punishment for his negligence is severe, as it is stated (Ecclesiastes 5:5), “Don’t let your mouth bring your flesh to sin, and don’t plead before the messenger that it was an error, but fear God; else God may be angered by your talk and destroy the work of your hands.” Its explanation is “Don’t let your mouth bring your flesh to sin, etc.” - why do you vow, if you are not careful with your vows and bring guilt upon yourself? And we have already explained this verse in the Gates of Precautions of Caution (no longer extant). And our Rabbis, may their memory be blessed, have said about the iniquity of [unfulfilled] vows (Shabbat 32b) that children die [as a result], as it is stated (Ecclesiastes 5:5), “and destroy the work of your hands.” The verse is also explained to be about the matter of evil speech, that one is punished for negligence with it - even if he does not intend to disgrace his fellow. (And likewise did our Rabbis, may their memory be blessed, say in the Sifrei - and Rashi cites it in his commentary on the Torah concerning Miriam - and this is its language, “And with Miriam, she did not have in mind to to disgrace him [...]” And it concludes in the Sifrei, “But rather for praise, on account of the commandment of being fruitful and multiplying, etc.”) And behold we were commanded not to make vows, as it is stated (Deuteronomy 23:23) “Whereas you incur no guilt if you refrain from vowing.” And our Rabbis expounded from this (Nedarim 77b) that if one does vow, he incurs guilt. For a vow is a stumbling block for the one who vows, lest he profane his word or delay fulfilling it. Rather a righteous man is gracious and gives without his vowing. [It is hence forbidden to vow] except for when he calls out from distress. For then he should make a vow, like the matter that is written (Genesis 28:20), “And Jacob made a vow, saying, etc.” And likewise in the gathering together of the heads of the people - the Tribes of Israel: They should make vows to strengthen weakened hands. (It appears to me that his intention in that which he wrote, “to strengthen weakened hands,” is meaning to say that it energizes the rest of the people whose hands are weakened in the trait of volunteering, since they are not used to it. And through his vowing publicly in front of many people, their hearts are elevated to volunteer as well. And so is it written in I Chronicles 29:1-9, “King David said to the entire assemblage, etc. ‘I have prepared with all of my strength, etc. and who is going to make a freewill offering and devote himself today to the Lord?’ And the officers of the clans made freewill offerings, etc. The people rejoiced over the freewill offerings they made, for with a whole heart they made freewill offerings to the Lord; King David also rejoiced very much.”

Therefore, I exhort you to train yourself to sit as much as possible, because the sin of the tongue is the most severe, as our Sages said (Tosefta Pe'ah 1): "These are the things...and lashon hara is equivalent to them all." I don't have to elaborate on this most serious sin of all. "All man's toil is for his mouth" (Koheles 6:7). Our Sages said that all man's mitzvos and teachings are not enough to counterbalance what comes out of his mouth. "What should be a man's pursuit in this world? He should be silent" (Chullin 89a). One must seal his lips as tight as two millstones. Idle words are like powerful weapons which can reach from one end of the world to the other. Now, this is true concerning mere excessive speech. Where forbidden speech is concerned - e.g. lashon hara, mocking, swearing, vowing, fighting and cursing - especially in the synagogue, and on Shabbos and Yom Tov - for every utterance of this type it is impossible to imagine the pain and suffering one will receive (Zohar)! No word is lost; everything is recorded. Winged beings attach themselves to everyone, recording all they say. "For a bird of the skies may carry the sound, and some winged creature may tell the matter" (Koheles 10:20). "Let not your mouth cause your flesh to sin, and do not tell the messenger that it was an error. Why should G-d be angered by your speech and destroy the work of your hands?" (ibid. 5:5). Purchase all your needs through a messenger, even if this would cost two or three times as much. "Is there a limit to what G-d can provide?" (Bamidbar 11:23). Hashem feeds all creatures, from the greatest to the smallest (see A.Z. 3), and provides all their needs. And on Shabbos and Yom Tov do not speak at all about things that are not urgent, and be brief even with what is important, for the Shabbos is very holy and our Sages barely permitted the exchange of greetings on it (Yerushalmi Shabbos, and Tosfos Shab. 113). See how strict they were concerning even a single expression! Continue to give great honor to the Shabbos as when I was there. Do not cut back [on your Shabbos] expenses, since "Man's entire sustenance [for the year is fixed for him from Rosh Hashana to Yom Kippur,] except [the expenditure for Sabbaths and Festivals,] etc." (Beitzah 16a).

And they also expounded (in Vayikra Rabbah 16) the verse (Koheleth 5:5): "Do not allow your mouth to cause sin to your flesh" — do not speak lashon hara with your mouth to punish all of your flesh with this sin. The Rabbis applied this verse to Miriam: "Do not allow your mouth" — you, Miriam, as it is written (Numbers 12:10): "And, behold, Miriam was leprous, [white] as snow." (Koheleth, Ibid.): "that it was an error" — as it is written (Numbers 12:11): "wherein we [(Aaron and Miriam)] have erred and wherein we have sinned." (Koheleth, Ibid.): "Why should G-d be angry at your voice?" — at the lashon hara you have spoken against Moses, as it is written (Numbers 12:9): "and the anger of the L-rd burned against them, and He departed." (Koheleth, Ibid.): "and [He shall] destroy the work of your hands." R. Yochanan said: "With her mouth she sinned, and all her limbs were smitten, as it is written (Numbers 12:10): 'And the cloud departed from the tent, and, behold, Miriam was leprous, [white] as snow.' This is the intent of: "Do not allow your mouth to cause sin to [destroy] your flesh" … (Mishlei 21:33): 'He who guards his mouth and his tongue guards his soul from troubles.'"