Rosh Hashanah 16a
ראש השנה ט״ז א — ד"ה וּמִפְּנֵי מָה אָמְרָה תּוֹרָה נַסְּכוּ מַיִם
Rosh Hashanah 16a:15
The shofar is connected with remembrance, repentance, and the binding of Isaac; its sound evokes Abraham’s ram and Israel’s willingness to return to God.
וּמִפְּנֵי מָה אָמְרָה תּוֹרָה נַסְּכוּ מַיִם בֶּחָג — אָמַר הַקָּדוֹשׁ בָּרוּךְ הוּא: נַסְּכוּ לְפָנַי מַיִם בֶּחָג, כְּדֵי שֶׁיִּתְבָּרְכוּ לָכֶם גִּשְׁמֵי שָׁנָה. וְאִמְרוּ לְפָנַי בְּרֹאשׁ הַשָּׁנָה מַלְכִיּוֹת זִכְרוֹנוֹת וְשׁוֹפָרוֹת. מַלְכִיּוֹת — כְּדֵי שֶׁתַּמְלִיכוּנִי עֲלֵיכֶם, זִכְרוֹנוֹת — כְּדֵי שֶׁיַּעֲלֶה זִכְרוֹנְיכֶם לְפָנַי לְטוֹבָה, וּבַמֶּה — בְּשׁוֹפָר. אָמַר רַבִּי אֲבָהוּ: לָמָה תּוֹקְעִין בְּשׁוֹפָר שֶׁל אַיִל? אָמַר הַקָּדוֹשׁ בָּרוּךְ הוּא: תִּקְעוּ לְפָנַי בְּשׁוֹפָר שֶׁל אַיִל, כְּדֵי שֶׁאֶזְכּוֹר לָכֶם עֲקֵידַת יִצְחָק בֶּן אַבְרָהָם, וּמַעֲלֶה אֲנִי עֲלֵיכֶם כְּאִילּוּ עֲקַדְתֶּם עַצְמְכֶם לְפָנַי.
And for what reason did the Torah say: Pour water onto the altar in the Temple on the festival of Sukkot? The Holy One, Blessed be He, said: Pour water before Me on the festival of Sukkot so that the rains of the year, which begin to fall after Sukkot, will be blessed for you. And recite before Me on Rosh HaShana verses that mention Kingships, Remembrances, and Shofarot: Kingships so that you will crown Me as King over you; Remembrances so that your remembrance will rise before Me for good; and with what will the remembrance rise? It will rise with the shofar. Similarly, Rabbi Abbahu said: Why does one sound a blast with a shofar made from a ram’s horn on Rosh HaShana? The Holy One, Blessed be He, said: Sound a blast before Me with a shofar made from a ram’s horn, so that I will remember for you the binding of Isaac, son of Abraham, in whose stead a ram was sacrificed, and I will ascribe it to you as if you had bound yourselves before Me.