Why do we do Tashlich?
(יח) מִי־אֵ֣ל כָּמ֗וֹךָ נֹשֵׂ֤א עָוֺן֙ וְעֹבֵ֣ר עַל־פֶּ֔שַׁע לִשְׁאֵרִ֖ית נַחֲלָת֑וֹ לֹא־הֶחֱזִ֤יק לָעַד֙ אַפּ֔וֹ כִּֽי־חָפֵ֥ץ חֶ֖סֶד הֽוּא׃ (יט) יָשׁ֣וּב יְרַֽחֲמֵ֔נוּ יִכְבֹּ֖שׁ עֲוֺֽנֹתֵ֑ינוּ וְתַשְׁלִ֛יךְ בִּמְצֻל֥וֹת יָ֖ם כָּל־חַטֹּאותָֽם׃ (כ) תִּתֵּ֤ן אֱמֶת֙ לְיַֽעֲקֹ֔ב חֶ֖סֶד לְאַבְרָהָ֑ם אֲשֶׁר־נִשְׁבַּ֥עְתָּ לַאֲבֹתֵ֖ינוּ מִ֥ימֵי קֶֽדֶם׃

(18) Who is a God like You, Forgiving iniquity And remitting transgression; Who has not maintained His wrath forever Against the remnant of His own people, Because He loves graciousness! (19) He will take us back in love; He will cover up our iniquities, You will hurl all our sins Into the depths of the sea. (20) You will keep faith with Jacob, Loyalty to Abraham, As You promised on oath to our fathers In days gone by.

(א) וַיֵּאָסְפ֤וּ כָל־הָעָם֙ כְּאִ֣ישׁ אֶחָ֔ד אֶל־הָ֣רְח֔וֹב אֲשֶׁ֖ר לִפְנֵ֣י שַֽׁעַר־הַמָּ֑יִם וַיֹּֽאמְרוּ֙ לְעֶזְרָ֣א הַסֹּפֵ֔ר לְהָבִ֗יא אֶת־סֵ֙פֶר֙ תּוֹרַ֣ת מֹשֶׁ֔ה אֲשֶׁר־צִוָּ֥ה יְהוָ֖ה אֶת־יִשְׂרָאֵֽל׃
(1) the entire people assembled as one man in the square before the Water Gate, and they asked Ezra the scribe to bring the scroll of the Teaching of Moses with which the LORD had charged Israel.
וַיֹּ֣אמֶר שְׁמוּאֵ֔ל קִבְצ֥וּ אֶת־כָּל־יִשְׂרָאֵ֖ל הַמִּצְפָּ֑תָה וְאֶתְפַּלֵּ֥ל בַּעַדְכֶ֖ם אֶל־יְהוָֽה׃ וַיִּקָּבְצ֣וּ הַ֠מִּצְפָּתָה וַיִּֽשְׁאֲבוּ־מַ֜יִם וַֽיִּשְׁפְּכ֣וּ ׀ לִפְנֵ֣י יְהוָ֗ה וַיָּצ֙וּמוּ֙ בַּיּ֣וֹם הַה֔וּא וַיֹּ֣אמְרוּ שָׁ֔ם חָטָ֖אנוּ לַיהוָ֑ה וַיִּשְׁפֹּ֧ט שְׁמוּאֵ֛ל אֶת־בְּנֵ֥י יִשְׂרָאֵ֖ל בַּמִּצְפָּֽה׃
Samuel said, “Assemble all Israel at Mizpah, and I will pray to the LORD for you.” They assembled at Mizpah, and they drew water and poured it out before the LORD; they fasted that day, and there they confessed that they had sinned against the LORD. And Samuel acted as chieftain of the Israelites at Mizpah.

(ב) אוֹכְלִים רֹאשׁ כֶּבֶשׂ לוֹמַר: נִהְיֶה לְרֹאשׁ וְלֹא לְזָנָב, וְזֵכֶר לְאֵילוֹ שֶׁל יִצְחָק. הַגָּה: יֵשׁ מְדַקְדְּקִים שֶׁלֹּא לֶאֱכֹל אֱגוֹזִים, שֶׁאֱגוֹז בְּגִימַטְרִיָּא חֵטְא, וְעוֹד שֶׁהֵן מַרְבִּים כִּיחָה וְנִיעָה וּמְבַטְּלִים הַתְּפִלָּה (מַהֲרִי''ל). וְהוֹלְכִין אֶל הַנָּהָר לוֹמַר פָּסוּק: וְתַשְׁלִיךְ בִּמְצֻלוֹת יָם כָּל חַטֹּאותָם וְגוֹ' (מִיכָה ז, יט) (מִנְהָגִים). וְגַם נוֹהֲגִים שֶׁלֹּא לִישַׁן בְּיוֹם רֹאשׁ הַשָּׁנָה (יְרוּשַׁלְמִי), וּמִנְהָג נָכוֹן הוּא.

(2) Eat a head of a lamb saying: Let us be as a head and not a tail. It is also a remembrance of the ram of Isaac. Rema: There are those who are careful not to eat nuts, as the word "egoz" in gematriah [is equal to the value of] chet (sin). They also cause a lot of excess saliva and phloem and cause abrogation of prayers. They also go to a river and say the verse: And Thou wilt cast all their sins into the depths of the sea (Micah 7:19). There are also those who do not sleep during Rosh Hashana during the day, and this is the correct thing to do.

הָאוֹמֵר, אֶחֱטָא וְאָשׁוּב, אֶחֱטָא וְאָשׁוּב, אֵין מַסְפִּיקִין בְּיָדוֹ לַעֲשׂוֹת תְּשׁוּבָה. אֶחֱטָא וְיוֹם הַכִּפּוּרִים מְכַפֵּר, אֵין יוֹם הַכִּפּוּרִים מְכַפֵּר. עֲבֵרוֹת שֶׁבֵּין אָדָם לַמָּקוֹם, יוֹם הַכִּפּוּרִים מְכַפֵּר. עֲבֵרוֹת שֶׁבֵּין אָדָם לַחֲבֵרוֹ, אֵין יוֹם הַכִּפּוּרִים מְכַפֵּר, עַד שֶׁיְּרַצֶּה אֶת חֲבֵרוֹ. אֶת זוֹ דָּרַשׁ רַבִּי אֶלְעָזָר בֶּן עֲזַרְיָה, מִכֹּל חַטֹּאתֵיכֶם לִפְנֵי יְיָ תִּטְהָרוּ (ויקרא טז), עֲבֵרוֹת שֶׁבֵּין אָדָם לַמָּקוֹם, יוֹם הַכִּפּוּרִים מְכַפֵּר. עֲבֵרוֹת שֶׁבֵּין אָדָם לַחֲבֵרוֹ, אֵין יוֹם הַכִּפּוּרִים מְכַפֵּר, עַד שֶׁיְּרַצֶּה אֶת חֲבֵרוֹ. אָמַר רַבִּי עֲקִיבָא, אַשְׁרֵיכֶם יִשְׂרָאֵל, לִפְנֵי מִי אַתֶּם מִטַּהֲרִין, וּמִי מְטַהֵר אֶתְכֶם, אֲבִיכֶם שֶׁבַּשָּׁמַיִם, שֶׁנֶּאֱמַר (יחזקאל לו), וְזָרַקְתִּי עֲלֵיכֶם מַיִם טְהוֹרִים וּטְהַרְתֶּם. וְאוֹמֵר (ירמיה יז), מִקְוֵה יִשְׂרָאֵל יְיָ, מַה מִּקְוֶה מְטַהֵר אֶת הַטְּמֵאִים, אַף הַקָּדוֹשׁ בָּרוּךְ הוּא מְטַהֵר אֶת יִשְׂרָאֵל:

One who says: I shall sin and repent, sin and repent, they do not afford him the opportunity to repent. [If one says]: I shall sin and Yom HaKippurim will atone for me, Yom HaKippurim does not effect atonement. For transgressions between man and God Yom HaKippurim effects atonement, but for transgressions between man and his fellow Yom HaKippurim does not effect atonement, until he has pacified his fellow. This was expounded by Rabbi Elazar b. Azariah: “From all your sins before the Lord you shall be clean” (Leviticus 16:30) for transgressions between man and God Yom HaKippurim effects atonement, but for transgressions between man and his fellow Yom HaKippurim does not effect atonement, until he has pacified his fellow. Rabbi Akiva said: Happy are you, Israel! Who is it before whom you become pure? And who is it that purifies you? Your Father who is in heaven, as it is said: “And I will sprinkle clean water upon you and you shall be clean” (Ezekiel 36:25). And it further says: “O hope (mikveh) of Israel, O Lord” (Jeremiah 17:1--just as a mikveh purifies the unclean, so too does he Holy One, blessed be He, purify Israel.)

(יב) בַּיּוֹם הַשְּׁלִישִׁי. וְכִי מֵאַחַר שֶׁהַדֶּרֶךְ קְרוֹבָה, לָמָּה נִתְעַכֵּב שְׁלֹשֶׁת יָמִים. כֵּיוָן שֶׁרָאָה שֶׁלֹּא קִבְּלוּ מִמֶּנּוּ הָלַךְ וְנַעֲשָׂה לִפְנֵיהֶם נָהָר גָּדוֹל. מִיָּד יָרַד אַבְרָהָם לְתוֹךְ הַמַּיִם וְהִגִּיעוּ עַד בִּרְכָּיו. אָמַר לִנְעָרָיו בּוֹאוּ אַחֲרַי, יָרְדוּ אַחֲרָיו. כֵּיוָן שֶׁהִגִּיעוּ עַד חֲצִי הַנָּהָר, הִגִּיעוּ הַמַּיִם עַד צַוָּארוֹ. בְּאוֹתָהּ שָׁעָה תָּלָה אַבְרָהָם עֵינָיו לַשָּׁמַיִם, אָמַר לְפָנָיו: רִבּוֹנוֹ שֶׁל עוֹלָם, בְּחַרְתָּנִי וְהוֹרֵתָנִי וְנִגְלֵיתָ לִי וְאָמַרְתָּ לִי, אֲנִי יָחִיד וְאַתָּה יָחִיד, עַל יָדְךָ יִוָּדַע שְׁמִי בְעוֹלָמִי וְהַעֲלֵה יִצְחָק בִּנְךָ לְפָנַי לְעוֹלָה וְלֹא עִכַּבְתִּי. וַהֲרֵינִי עוֹסֵק בְּצִוּוּיֶךָ, וְעַכְשָׁו בָּאוּ מַיִם עַד נָפֶשׁ. אִם אֲנִי אוֹ יִצְחָק בְּנִי טוֹבֵעַ, מִי יְקַיֵּם מַאֲמָרְךָ. עַל מִי יִתְיַחֵד שְׁמֶךָ. אָמַר לוֹ הַקָּדוֹשׁ בָּרוּךְ הוּא, חַיֶּיךָ, שֶׁעַל יָדְךָ יִתְיַחֵד שְׁמִי בָּעוֹלָם. מִיָּד גָּעַר הַקָּדוֹשׁ בָּרוּךְ הוּא אֶת הַמַּעְיָן וְיָבַשׁ הַנָּהָר וְעָמְדוּ בַיַּבָּשָׁה.

(12) On the third day Abraham lifted up his eyes (ibid., v. 4). Since the distance was extremely short, what delayed them three days? When Satan realized that they would not pay any attention to him, he went ahead and created a river in their path. When Abraham stepped into the river, it reached his knees. He ordered his young men to follow him, and they did so. But in the middle of the river the water reached his neck. Thereupon, Abraham lifted his eyes heavenward and cried out: Master of the Universe, You have chosen me; You have instructed me; You revealed Yourself to me; You have declared: I am one and You are one, and through You shall my name be made known in My world. You have ordered me: Offer, Isaac, thy son, as a sacrifice, and I did not refuse; but now, as I am about to fulfill Thy command, these waters endanger my life. If either I or my son, Isaac, should drown, who will fulfill Your decrees, and who will proclaim the Unity of Your Name? The Holy One, blessed be He, responded: Be assured that through you the Unity of My Name will be made known through the world. Thereupon the Holy One, blessed be He, rebuked the source of the water, and caused the river to dry up. Once again, they stood on dry land.

(ח) (ח) הנהר וכו' - ולומר תשוב תרחמנו וגו'. משום דאיתא במדרש שעבר אברהם אבינו עד צוארו במים כשהלך להקריבו ע"ג המזבח ואמר הושיעה כי באו מים עד נפש ואנו עושין זה זכר לעקידה. וטוב למקום שיש בו דגים חיים לסימן שלא תשלוט בנו עין הרע ונפרה ונרבה כדגים. ובכתבים כתב נהר או באר וטוב שיהיה מחוץ לעיר.

Because there is a Midrash that Abraham crossed the river up to his neck when he went to go sacrifice his son Isaac. He then said, (from Psalms 69:2): Save me, O God, for water has come up to my soul. So we do Tashlich as a way of remembering the Akeidah/binding of Isaac. And it is good if it is a place that has living fish as a sign that the evil eye should not fall upon us and we should be able to multiply like fish, as fish are incapable of being affected by the evil eye. And in the writings it says at a river or well, and it is good if it is outside the city.

וְטוֹב שֶׁיִּהְיֶה מִחוּץ לָעִיר וְיֶשׁ בּוֹ דָּגִּים (לְזֵכֶר שֶׁאָנוּ מְשׁוּלִים כְּדָגִים חַיִּים הַלָּלוּ שֶׁנֶּאֱחָזִים בַּמְּצוֹדָה, כָּךְ אָנוּ נֶאֱחָזִים בִּמְצוּדַת הַמָּוֶת וְהַדִּין, וּמִתּוֹךְ כָּךְ נְהַרְהֵר יוֹתֵר בִּתְשׁוּבָה. עוֹד טַעַם, סִימָן שֶׁלֹּא תִשְׁלֹט בָּנוּ עַיִן רָעָה כְּמוֹ בְּדָגִים, וְנִפְרֶה וְנִרְבֶּה כְּדָגִים. וְיֵשׁ אוֹמְרִים, הַטַּעַם, כִּי לְדָגִים אֵין גְּבִינִים [עַפְעַפַּיִם] וְעֵינֵיהֶם תָּמִיד פְּתוּחוֹת, כְּדֵי לְהִתְעוֹרֵר עֵינָא פְּקִיחָא דִּלְעֵילָא) וְאִם אֵין שָׁם נָהָר שֶׁיֵּשׁ בּוֹ דָּגִּים, הוֹלְכִין לְנָהָר אַחֵר אוֹ לִבְאֵר, וְאוֹמְרִים הַפְּסוּקִים מִי אֵל כָּמוֹךָ וְכוּ' כַּכָּתוּב בַּסִּדּוּרִים בְּסֵדֶר תַּשְׁלִיךְ. וּמְנַעֲרִים שׁוּלֵי הַבְּגָדִים, וְהוּא לְרֶמֶז בְּעָלְמָא, לִתֵּן לֵב לְהַשְׁלִיךְ אֶת הַחֲטָאִים וּלְחַפֵּשׂ וְלַחֲקֹר דְּרָכָיו מֵהַיּוֹם וָהָלְאָה, שֶׁיִּהְיוּ בְּגָדָיו לְבָנִים וּנְקִיִּים מִכָּל חֵטְא. אִם חָל יוֹם רִאשׁוֹן בַּשַׁבָּת הוֹלְכִין בְּיוֹם שֵׁנִי (תקפג ובסידור).

It is preferable that [this river] should be outside the city limits and it should contain fish (as a reminder that we are compared to living fish who are caught in a net. We too, are caught in the net of death and judgment, and as a result [we will be inclined] to think more of repenting. Another reason is to symbolize that the evil eye shall have no power over us, just as [it has no power] over fish, and that we may be fruitful and multiply as the fish. Others say the reason is that fish have no eyelids, and their eyes are always open, the purpose is thus to arouse the compassion of the All-Seeing Eye above us.) But if there is no river that contains fish you may go to any river, or to a well, and you should recite the verses, Mi keil kamocha [Who, Almighty, is like you] etc. as it is written in the prayer books in the text of Tashlich. You should then shake the ends of your clothes, symbolizing your resolve to cast away your sins, and to examine and scrutinize your ways, from now on; so that your "clothes" will be white and innocent of all sin. If the first day of Rosh Hashanah is on Shabbos you go [to the stream for Tashlich] on the second day.

ומנהג של ישראל תורה הוא, במה שהולכים על מים ואמרים תשליך במצולת ים הוא התהום, והיא המקום היותר עמוק בים. והנה לפי הטבע של היסודות שהמים יכסו הארץ, והארץ הוא המרכז, והוא מקום הנמוך בכל העולם, והנה התגלות הארץ לצורך בני אדם ולדרים עליה אינו בלא כוונת מכוון והוא אשר חדש העולם כרצונו לתכלית ישוב הארץ, ולכן אנו הולכים על המים לראות אשר שם חול גבול לים, ואמר עד פה תבא ולא תוסף, וכשאנו הולכים שם אנו רואים גבורתו של יוצר בראשית, ולכן אנו הולכים על המים בראש השנה, שהוא יום הדין, לשום כל אחד על נפשו ענין בריאת העולם, ושהשם יתעלה מלך הארץ ועל זה נאמר תשליך במצולת ים חטאינו.

The custom of the Jewish people is law, that we go to the water and say tashlich at the abyss of a deep sea. It is the nature of the elements that water covers the land, for land is in the center [of the earth] is below the waters. The land was revealed [out of the sea] for the needs of mankind and creatures who dwell on it. This was certainly not unintentional, for He created the earth, according to His will for people to live on it. Therefore, we go to the water to see there the sand bordering the sea. We say, until here we can walk and no further. When we go there we see the strength of the Creator. This is why we come to the water on Rosh Hashanah, Judgement Day, [to realize that] because of every individual the world was created. G-d is the king of the world and for this we say, we send our sins into the depths of the sea.

ת"ר אין מושחים את המלכים אלא על המעיין כדי שתמשך מלכותם שנא' (מלכים א א, לג) ויאמר המלך להם קחו עמכם את עבדי אדוניכם [וגו'] והורדתם אותו אל גחון
The Sages taught: One anoints the kings only upon a spring, as an omen, so that their kingdom will continue like a spring, as it is stated with regard to the coronation of Solomon before the death of David: “And the king said unto them: Take with you the servants of your lord, and let Solomon my son ride upon my own mule, and bring him down to Gihon. And let Tzadok the priest and Nathan the prophet anoint him there king over Israel and sound the shofar and say: Long live King Solomon” (I Kings 1:33–34).

Tashlich - The Complement of Shofar, Rav Asher Meir

The theme of shofarot, mentioned in the prayers, is translated into action by the practical mitzva of shofar - the principle mitzva of the day. Of course, the shofar also gives expression to the other two themes: the ram's horn reminds us of the ram sacrificed in place of Yitzchak, and the shofar blast reminds us of a coronation fanfare. (See, for example, I Melakhim 1:34, 1:39.) That is why the shofar is blown during these benedictions as well as during the benediction of "shofarot."

But unlike the "shofarot," these motifs of sovereignty and memory have no practical mitzva which is unique to them. To that extent, we can view the custom of tashlikh as the complement of the mitzva of shofar. Balancing the shofar, which is the practical expression of the "shofarot" blessing, tashlikh gives a practical expression to the malkuyot/zikhronot pair.

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It is also appropriate that precisely these two themes find their practical expression in "minhag" (custom), rather than in a mitzva.

First of all, unlike shofar which is explicitly mentioned in the Torah, these "sovereignty" and "remembrance" aspects of Rosh Ha-shana are inferred from subtle textual hints. It is only natural that their practical expression should also be in the more subtle area of minhag.

Second of all, there is an important difference between the theme of shofar and those of malkhuyot and zikhronot. This difference is illustrated by a well-known Midrash which explains the relationship between the three foci of the Rosh Ha-shana Musaf:

"Why did the Sages ordain to say malkhuyot first, then zikhronot and shofarot? First of all make Him King over you, and then ask for mercy so that He will remember you. And with what [will He remember]? With the shofar of liberation! But I still don't know who blows this shofar, so the Scripture teaches, 'And the Lord God will sound the shofar' (Zekharia 9:14)." (Sifri, Bamidbar 77)

This Midrash teaches that the WE are responsible for expressing the aspects of malkhuyot and zikhronot. We make God into our King, and ask for His mercy to be favorably remembered. So it is appropriate that the observance corresponding to malkhuyot and zikhronot should come from us - from the domain minhag.

In response, we hope and pray that God will react by blowing the shofar of liberation, i.e. by bringing the Redemption. So it is appropriate that the observance corresponding to shofarot comes from God, as a mitzva of the Torah.

It is also fitting that the mitzva of shofar is primarily a passive one - most people hear the shofar from the "ba'al toke'a," and the blessing recited is "to hear the sound of the shofar." This recalls the shofar of redemption which God will sound for us.

But the custom of tashlikh is performed by each person individually - corresponding to the responsibility of each individual to accept God's sovereignty and ask for His mercy.

So the beloved, but little-studied, custom of "tashlikh" provides a beautiful example of how the customs which were initiated by the Jewish people constitute a harmonious complement to the mitzvot of the Torah.