(Devarim 23:23) "But if you forbear to vow, it will not be a sin in you": R. Meir says: It is better not to vow than to vow and pay. Better than both (i.e., to vow and not to pay and to vow and to pay) is not to vow at all. R. Yehudah says: Better than both (i.e., to vow and not to pay and not to vow at all) is to vow and to pay. (Ibid. 24) "What issues from your lips shall you keep and you shall do":
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(דברים כג כד) מוֹצָא שְׂפָתֶיךָ, מִצְוַת עֲשֵׂה.
"What issues from your lips" — a positive commandment.
(דברים כג כג) וְכִי תֶחְדַּל לִנְדֹּר, רַבִּי מֵאִיר אוֹמֵר (קהלת ה ד): ״טוֹב אֲשֶׁר לֹא תִדֹּר מִשֶּׁתִּדֹּר וְלֹא תְשַׁלֵּם״, טוֹב מִזֶּה וּמִזֶּה שֶׁלֹּא תִדֹּר כָּל עִקָּר. רַבִּי יְהוּדָה אוֹמֵר: ״טוֹב אֲשֶׁר לֹא תִדֹּר״, טוֹב מִזֶּה וּמִזֶּה נוֹדֵר וּמְשַׁלֵּם.
(Devarim 23:23) "But if you forbear to vow, it will not be a sin in you": R. Meir says: It is better not to vow than to vow and pay. Better than both (i.e., to vow and not to pay and to vow and to pay) is not to vow at all. R. Yehudah says: Better than both (i.e., to vow and not to pay and not to vow at all) is to vow and to pay. (Ibid. 24) "What issues from your lips shall you keep and you shall do":
(דברים כג כד) מוֹצָא שְׂפָתֶיךָ, מִצְוַת עֲשֵׂה.
"What issues from your lips" — a positive commandment.
תִּשְׁמֹר, מִצְוַת לֹא תַעֲשֶׂה.
"shall you keep" — a negative commandment.
וְעָשִׂיתָ, הֲרֵי זוֹ אַזְהָרָה לְבֵית דִּין שֶׁיְּעַשּׂוּךָ.
"and you shall do": This is an exhortation to beth-din to make you do (what you have vowed).
כַּאֲשֶׁר נָדַרְתָּ, זֶה נֵדֶר.
"as you have vowed": This is a vow;
לַה׳ אֱלֹהֶיךָ, אֵלּוּ עֲרָכִים וַחֲרָמִים וְהֶקְדֵּשׁוֹת.
"to the L-rd your G-d": These are sin-offerings, guilt-offerings, burnt-offerings, and peace-offerings;
נְדָבָה, זוֹ נְדָבָה.
"the pledge": as implied;
אֲשֶׁר דִּבַּרְתָּ, זֶה הֶקְדֵּשׁ בֶּדֶק הַבַּיִת.
"that you spoke": These are consecrations for Temple maintenance;
בְּפִיךָ, זוֹ צְדָקָה.
"with you mouth": This is charity.