וְעוֹד כְּדִכְתִיב אִישׁ כִּי יָמוּת וּבֵן אֵין לוֹ And furthermore, the verse first states that a son inherits from his father, as it is written in the portion concerning inheritance: “If a man dies, and has no son, then you shall pass his inheritance to his daughter” (Numbers 27:8).
וְתַנָּא אַיְּידֵי דְּאָתְיָא לֵיהּ מִדְּרָשָׁא חֲבִיבָא לֵיהּ The Gemara answers: And as for the tanna of the mishna who listed the father inheriting first, since the halakha that a father inherits from his son is learned through a derivation and is not explicitly mentioned in the verse, this halakha is dear to him; therefore, he listed it first.
וּמַאי דְּרָשָׁא דְּתַנְיָא שְׁאֵרוֹ זֶה הָאָב מְלַמֵּד שֶׁהָאָב קוֹדֶם לָאַחִין יָכוֹל יְהֵא קוֹדֶם לַבֵּן תַּלְמוּד לוֹמַר הַקָּרוֹב קָרוֹב קָרוֹב קוֹדֵם And what is the derivation? As it is taught in a baraita concerning the verse: “And if his father has no brothers, then you shall give his inheritance to his kinsman who is next to him of his family, and he shall inherit it” (Numbers 27:11): “His kinsman”; this is referring to the father, and the Torah teaches that the father precedes the brothers of the deceased in inheriting from him. One might have thought that the father of the deceased should precede the son of the deceased in inheriting from him; the verse therefore states: “Next [hakkarov] to him,” teaching that the closer [karov] one is to the deceased, the earlier one is in the order of inheritance, and a son of the deceased is considered to be a closer relative to the deceased than the father of the deceased.
וּמָה רָאִיתָ לְרַבּוֹת אֶת הַבֵּן וּלְהוֹצִיא אֶת הָאָח מְרַבֶּה אֲנִי אֶת הַבֵּן שֶׁכֵּן קָם תַּחַת אָבִיו לִיעִדָה וְלִשְׂדֵה אֲחוּזָּה The Gemara asks: And what did you see to include the son as the closer relative than the father and to exclude the brother? The Gemara answers: I include the son, as he stands in place of his father to designate a Hebrew maidservant as a wife for himself, which a brother cannot do. And similarly, he stands in place of his father with regard to an ancestral field. If a son redeems a field consecrated by his father, it is considered as though the father himself redeemed it and the field returns to the family in the Jubilee Year. By contrast, if the brother of the one who consecrated it redeems the field, it does not return to the family (see Leviticus 27:16–21).
אַדְּרַבָּה מְרַבֶּה אֲנִי אֶת הָאָח שֶׁכֵּן קָם תַּחַת אָחִיו לְיִבּוּם כְּלוּם יֵשׁ יִבּוּם אֶלָּא בְּמָקוֹם שֶׁאֵין בֵּן הָא בְּמָקוֹם שֶׁיֵּשׁ בֵּן אֵין יִבּוּם The Gemara asks: On the contrary, I should include the brother as the closer relative, as he stands in his brother’s place with regard to levirate marriage, and a son does not. The Gemara answers: This is not a valid claim, as is there levirate marriage except in a case where there is no son? In a case where there is a son, there is no levirate marriage. This indicates that a son stands in place of the deceased before a brother even with regard to levirate marriage.
טַעְמָא דְּאִיכָּא הַאי פִּירְכָא הָא לָאו הָכִי הֲוָה אָמֵינָא אָח עֲדִיף תִּיפּוֹק לֵיהּ The Gemara comments: The reason that a son is considered to be a closer relative than a brother is specifically due to this refutation, that where there is a son there is no levirate marriage. This indicates that without this refutation I would say that a brother is superior to a son in terms of how close a relative he is. The Gemara therefore asks: Why not derive that a son is closer to the deceased than a brother