כִּ֣י יְסִֽיתְךָ֡ אָחִ֣יךָ בֶן־אִ֠מֶּךָ אֽוֹ־בִנְךָ֨ אֽוֹ־בִתְּךָ֜ א֣וֹ ׀ אֵ֣שֶׁת חֵיקֶ֗ךָ א֧וֹ רֵֽעֲךָ֛ אֲשֶׁ֥ר כְּנַפְשְׁךָ֖ בַּסֵּ֣תֶר לֵאמֹ֑ר נֵֽלְכָ֗ה וְנַֽעַבְדָה֙ אֱלֹהִ֣ים אֲחֵרִ֔ים אֲשֶׁר֙ לֹ֣א יָדַ֔עְתָּ אַתָּ֖ה וַאֲבֹתֶֽיךָ׃
Si ton frère, l’enfant de ta mère, si ton fils ou ta fille, ta compagne ou l’ami de ton cœur vient secrètement te séduire, en disant: "Allons servir des dieux étrangers," que toi ni tes pères n’avez jamais connus,
Rashi
כי יסיתך IF [THY BROTHER …] ENTICE THEE — The term יסת always denotes to “stir up”, “to incite”, as it is said, (I Samuel 26:19) ”If it be the Lord that hath stirred thee up (הסיתך) against me” (Sifrei Devarim 87:2); inciter in O. F., Engl, to incite — i.e. that he induces one to act thus.
Chizkuni
אחיך בן אמך, “your brother, the son of your mother.” The same applies to “your brother, the son of your father;” the reason why the Torah chose as its example the brother, son of your mother,” is that normally the bonds to one’s mother are closer, and one is in the same house with one’s mother all the time, while the father is in the field or elsewhere outside the house, earning his livelihood. Moreover, brotherly love to one another is often tainted by the fact that one has to share the father’s inheritance with one’s brother of the father, but not with a brother of the same mother.
Da'at Zekenim
כי יסתך אחיך בן אמך, “If your brother, son of your mother, will attempt to entice you (to worship an idol);” The reason that the Torah adds the words: “son of your mother,” here is that it is likely that brothers of the same mother, i.e. the same womb, are closer to one another than brothers who only share the same father. Furthermore, sons of only the same father are likely to be hostile to one another for reasons of the eventual inheritance.