This mitzvah entry addresses the commandment framework surrounding ritual purity and immersion, summarizing the underlying purpose of mikveh laws. It provides a conceptual overview rather than a detailed legal ruling.
וּבְטַעַם הַמַּיִם שֶׁיְּטַהֲרוּ כָּל טָמֵא אֶחְשֹׁב עַל צַד הַפְּשָׁט כִּי הָעִנְיָן הוּא כְּדֵי שֶׁיִּרְאֶה הָאָדָם אֶת עַצְמוֹ אַחַר הַטְּבִילָה כְּאִלּוּ נִבְרָא בְּאוֹתָהּ שָׁעָה, כְּמוֹ שֶׁהָיָה הָעוֹלָם כֻּלּוֹ מַיִם טֶרֶם הֱיוֹת בּוֹ אָדָם, וּכְמוֹ שֶׁכָּתוּב (בראשית א ב) וְרוּחַ אֱלֹהִים מְרַחֶפֶת עַל פְּנֵי הַמָּיִם. וְיִתֵּן אֶל לִבּוֹ בַּדִּמְיוֹן כִּי כְּמוֹ שֶׁנִּתְחַדֵּשׁ בְּגוּפוֹ יְחַדֵּשׁ גַּם כֵּן פְּעֻלּוֹתָיו לְטוֹב, וְיַכְשִׁיר מַעֲשָׂיו וִידַקְדֵּק בְּדַרְכֵי הַשֵּׁם בָּרוּךְ הוּא. וְעַל כֵּן אָמְרוּ חֲכָמִים שֶׁלֹּא תִּכְשַׁר הַטָּהֳרָה בַּמַּיִם שֶׁבִּכְלִי רַק בְּמַיִם חַיִּים אוֹ מְכֻנָּסִין שֶׁהֵן עַל קַרְקַע וְלֹא בִּכְלִי. מִכָּל מָקוֹם כְּדֵי לָתֵת אֶל לִבּוֹ בְּמַחְשָׁבָה כְּאִלּוּ הָעוֹלָם כֻּלּוֹ מַיִם, וְהוּא נִתְחַדֵּשׁ בַּעֲלוֹתוֹ מֵהֶן, כְּמוֹ שֶׁאָמַרְנוּ. וְאִם יִהְיוּ הַמַּיִם בִּכְלִי אוֹ אֲפִלּוּ עָבְרוּ עַל כְּלִי, לֹא יִתָּכֵן הָעִנְיָן הַזֶּה שֶׁאָמַרְנוּ אֶל מַחְשֶׁבֶת הַטּוֹבֵל. כִּי יֵשׁ גְּבוּל אֶל כָּל אֲשֶׁר הוּא בִּכְלִי שֶׁהוּא מַעֲשֵׂה יְדֵי אָדָם, וְעַל כֵּן לֹא יַחְשֹׁב בְּטָבְלוֹ בַּכְּלִי כְּאִלּוּ כָּל הָעוֹלָם מַיִם כַּאֲשֶׁר בַּתְּחִלָּה, וְשֶׁהוּא נִתְחַדֵּשׁ לִשְׁעָתוֹ. וְהַשּׁוֹמֵעַ יִשְׁמַע וְהֶחָדֵל יֶחְדַּל (יחזקאל ג כז). מִדִּינֵי הַמִּצְוָה. מָה שֶׁאָמְרוּ זִכְרוֹנָם לִבְרָכָה (נגעים יד א) כֵּיצַד מְטַהֲרִין אֶת הַמְּצֹרָע? מֵבִיא מִזְרָק שֶׁל חֶרֶשׂ שֶׁהוּא חָדָשׁ וְנוֹתֵן לְתוֹכוֹ רְבִיעִית מַיִם חַיִּים הָרְאוּיִין לְקַדֵּשׁ אוֹתָם לְמֵי חַטָּאת. וְשִׁעוּר זֶה (סוטה טז ב) מִדִּבְרֵי סוֹפְרִים. וּמֵבִיא שְׁתֵּי צִפֳּרִים חַיּוֹת טְהֹרוֹת לְשֵׁם טָהֳרַת הַמְּצֹרָע, שֶׁנֶּאֱמַר (ויקרא יד ד) וְלָקַח לַמִּטַּהֵר. וְשׁוֹחֵט אֶת הַבְּרוּרָה (פי, מובחרת) שֶׁבִּשְׁתֵּיהֶן עַל הַמַּיִם שֶׁבִּכְלִי חֶרֶשׂ וּמְמַצֶּה עַד שֶׁיִּהְיֶה הַדָּם נִכָּר בַּמַּיִם, וְחוֹפֵר וְקוֹבֵר הַצִּפּוֹר הַשְּׁחוּטָה בְּפָנָיו, וְדָבָר זֶה קַבָּלָה מִפִּי הַשְּׁמוּעָה. וְנוֹטֵל עֵץ אֶרֶז, וּמִצְוָתוֹ שֶׁיְּהֵא אָרְכּוֹ אַמָּה וְעָבְיוֹ כִּרְבִיעַ כֶּרַע מִכַּרְעֵי הַמִּטָּה. וְאֵזוֹב שֶׁאֵין לוֹ שֵׁם לְוַי לֹא יְהֵא פָּחוֹת מִטֶּפַח. וּשְׁנִי תּוֹלַעַת מִשְׁקָלוֹ שֶׁקֶל, וְאִם טְעָמוֹ פְּסָלוֹ כִּצְבִיעַת הַתְּכֵלֶת שֶׁנִּפְסַל בִּטְעִימָה. וְכָל הַשִּׁעוּרִין (עירובין ד א) הֲלָכָה. וְלוֹקֵחַ עִם שְׁלָשְׁתָּן הַצִּפּוֹר הַחַיָּה. וְאַרְבַּעַת מִינִין אֵלֶּה מְעַכְּבִין זֶה אֶת זֶה (מנחות כז א). וְעֵץ אֶרֶז וְאֵזוֹב שֶׁנִּתְקַלְּפוּ פְּסוּלִין, וְכוֹרֵךְ הָאֵזוֹב עִם הָאֶרֶז בְּלָשׁוֹן שֶׁל זְהוֹרִית, וּמַקִּיף לָהֶם רָאשֵׁי אֲגַפַּיִם וְרֹאשׁ הַזָּנָב שֶׁל [הַ]צִּפּוֹר הַחַיָּה, וְטוֹבֵל אַרְבַּעְתָּן בַּמַּיִם שֶׁבַּכְּלִי וּבַדָּם שֶׁעֲלֵיהֶן, וּמַזֶּה שֶׁבַע פְּעָמִים עַל גַּב יָדוֹ שֶׁל מְצֹרָע וּמְשַׁלֵּחַ הַצִּפּוֹר. וְכֵיצַד מְשַׁלְּחָהּ? (קידושין נז ב) עוֹמֵד בָּעִיר וְזוֹרְקָהּ חוּץ לַחוֹמָה וְאֵינוֹ הוֹפֵךְ פָּנָיו לָאֹהָלִים וְלֹא לָעִיר אֶלָּא לַמִּדְבָּר, שֶׁנֶּאֱמַר (שם יד נג) אֶל מִחוּץ לָעִיר אֶל פְּנֵי הַשָּׂדֶה. שִׁלְּחָהּ וְחָזְרָה חוֹזֵר וּמְשַׁלְּחָהּ, אֲפִלּוּ מֵאָה פְּעָמִים.
And about the reason that water purifies everything impure, I would think on the side of the simple understanding that it is in order that a man see himself with the immersion as if he is created at that time, [just] like the whole world was water before man was upon it — as it is written (Genesis 1:2), “and the spirit of God floated upon the face of the waters.” And through this comparison, he shall place upon his heart that [just] like he is renewed in his body, he [must] also renew his actions for the good, fix his actions and be exacting in the way of God, blessed be He. And therefore the Sages said that the purification is not fit with water that is in a vessel, but rather only with living water — or collected [water], which is on the ground and, in any case, not in a vessel — in order to place in his heart the thought as if the world was entirely water, and [that] he is renewed with his emerging from them, as we said. But if the water was in a vessel — or even if it passed through a vessel — this matter that we said would not be set in the thought of the one immersing. As there is a limit to all that is in a vessel, which is the creation of the hands of man. And therefore when he immerses in a vessel, he will not think as if the whole world is water like at the beginning [of Creation], and that he is renewed at that time. ‘And the one who accepts, will accept; and the one who refrains will refrain.’ From the laws of the commandment is that which they, may their memory be blessed, said (Mishnah Negaim 14:1), “How does one purify the metsora? He would bring a new earthenware pitcher and place within it a reviit of living water,” with which it would be fitting to consecrate the sprinkling water — and that measure is [rabbinic] (Sotah 16b) — “and he would bring two wild birds” that are pure, for the sake of the purification of the metsora; as it is stated (Leviticus 14:4), “and it shall be taken for the one being purified.” He slaughters the clarified (meaning, choice) of the two of them upon the water in the earthenware vessel and squeezes until the blood is recognizable in the water. And he digs and buries the slaughtered bird before him — and this is a tradition from what was heard. He takes cedar wood — and its commandment is that it be an ell long and its width be like a quarter of a foot of the feet of a bed; and not less than a handbreadth of hyssop that does not have an adjunct name; wool dyed red, the weight of which is a shekel, and if he mixed [its color], he disqualified it, like the dying of the aquamarine, which is disqualified by mixing. And all the measures are a law [from Moshe at Sinai] (Eruvin 4a). And he takes the living bird with the three of them; and the four species impede one another (Menachot 27a); and cedar wood or hyssop that have been peeled are disqualified. He ties the hyssop to the cedar wood with a strip of crimson fabric and surrounds them with the tips of the wings and the tip of the tail of the living bird. And he dips the four of them in water that is in the vessel and in the blood that is [in] it; “and sprinkles seven times on the back of the hand of the metsora.” And he sends away the bird. And how does he send it away? If he is standing in the city, he throws it out of the wall (Kiddushin 57b). “He does not face the sea nor the city, but the desert, as it is stated (Leviticus 14:53), ‘to outside the city towards the field’” (Mishnah Negaim 14:2). [If] he sent it and it comes back, he again sends it away — even a hundred times.