(Devarim 21:4) "And the elders of that city shall bring the heifer down": I might think that this is (only) a mitzvah, (but not a categorical requirement); it is, therefore, written again "the elders of that city," after having been written before (verse 3), to make it a categorical requirement. From here they ruled: If the body were found near the border or near a city inhabited mostly by gentiles or near a city lacking a beth-din, they would not measure.
("And they shall bring the heifer down) to a hard river-bed": And whence is it derived that it is valid even if it is not hard? From (Ibid.) "in the river bed" — even if it is not hard.
("a hard river-bed) which shall not be worked": I might think that it is forbidden to comb flax there and to chisel stones there; it is, therefore, written "and which shall not be sowed." Sowing was included in all (labor). Why was it singled out? To make it a paradigm, viz.: Just as sowing is distinctly in the soil, so, all (such labors are forbidden), to exclude those which are not labors of the soil.
"and they shall break there the neck of the heifer": It is written here "breaking," and elsewhere (Vayikra 5:18) "breaking." Just as there, he breaks the neck with a hatchet from behind, so, here. "and they shall break there the neck": It is written here "there," and, elsewhere, "there." Just as there, he buries it and it is forbidden to derive benefit from it, so, here. [("a hard river-bed) which shall not be worked": I might think that it is forbidden to comb flax there and to chisel stones there; it is, therefore, written "and which shall not be sowed." Sowing was included in all (labor). Why was it singled out? To make it a paradigm, viz.: Just as sowing is distinctly in the soil, so, all (such labors are forbidden), to exclude those which are not labors of the soil.]
(דברים כא ד) וְהוֹרִידוּ זִקְנֵי הָעִיר הַהִיא – מִצְוָה בְּזִקְנֵי הָעִיר הַהִיא.
(Devarim 21:4) "And the elders of that city shall bring the heifer down": I might think that this is (only) a mitzvah, (but not a categorical requirement); it is, therefore, written again "the elders of that city," after having been written before (verse 3), to make it a categorical requirement. From here they ruled: If the body were found near the border or near a city inhabited mostly by gentiles or near a city lacking a beth-din, they would not measure.
אֶת הָעֶגְלָה אֶל נַחַל אֵיתָן – כְּמַשְׁמָעוֹ, קָשֶׁה; וְאַף עַל פִּי שֶׁאֵינוֹ אֵיתָן – כָּשֵׁר.
("And they shall bring the heifer down) to a hard river-bed": And whence is it derived that it is valid even if it is not hard? From (Ibid.) "in the river bed" — even if it is not hard.
עוֹרְפִים אוֹתָהּ בְּקוֹפִיץ מֵאֲחוֹרֶיהָ, וּמְקוֹמָהּ אָסוּר מִלִּזְרוֹעַ וּמִלַּעֲבוֹד. יָכוֹל יְהֵא אָסוּר לִסְרוֹק שָׁם פִּשְׁתָּן וּלְנַקֵּר שָׁם אֶת הָאֲבָנִים? תַּלְמוּד לוֹמַר: אֲשֶׁר לֹא יֵעָבֵד בּוֹ וְלֹא יִזָּרֵעַ, זְרִיעָה בִּכְלָל הָיְתָה, וְלָמָּה יָצָאת? לְהַקִּישׁ אֵלֶיהָ – מָה זְרִיעָה מְיֻחֶדֶת שֶׁהִיא עֲבוֹדַת קַרְקַע; יָצְאוּ אֵלּוּ, שֶׁאֵין עֲבוֹדַת קַרְקַע.
("a hard river-bed) which shall not be worked": I might think that it is forbidden to comb flax there and to chisel stones there; it is, therefore, written "and which shall not be sowed." Sowing was included in all (labor). Why was it singled out? To make it a paradigm, viz.: Just as sowing is distinctly in the soil, so, all (such labors are forbidden), to exclude those which are not labors of the soil.
וְעָרְפוּ שָׁם, נֶאֱמַר כָּאן עֲרִיפָה וְנֶאֱמַר לְהַלָּן (שמות יג יג) עֲרִיפָה, מָה עֲרִיפָה הָאֲמוּרָה כָּאן – עוֹרְפָהּ בְּקוֹפִיץ מֵאַחֲרֶיהָ, וְקוֹבְרָהּ, וַאֲסוּרָה בַּהֲנָיָה, אַף עֲרִיפָה הָאֲמוּרָה לְהַלָּן – עוֹרְפָהּ בְּקוֹפִיץ מֵאֲחוֹרֶיהָ, וְקוֹבְרָהּ, וַאֲסוּרָה בַּהֲנָיָה.
"and they shall break there the neck of the heifer": It is written here "breaking," and elsewhere (Vayikra 5:18) "breaking." Just as there, he breaks the neck with a hatchet from behind, so, here. "and they shall break there the neck": It is written here "there," and, elsewhere, "there." Just as there, he buries it and it is forbidden to derive benefit from it, so, here. [("a hard river-bed) which shall not be worked": I might think that it is forbidden to comb flax there and to chisel stones there; it is, therefore, written "and which shall not be sowed." Sowing was included in all (labor). Why was it singled out? To make it a paradigm, viz.: Just as sowing is distinctly in the soil, so, all (such labors are forbidden), to exclude those which are not labors of the soil.]
בַּנָּחַל – אַף עַל פִּי שֶׁאֵינוֹ אֵיתָן.
"in the river bed" — even if it is not hard.