ואני הנה לקחתי. וַאֲנִי מֵהֵיכָן זָכִיתִי בָהֶן מתוך בני ישראל שֶׁיִּהְיוּ יִשְׂרָאֵל שׂוֹכְרִין אוֹתָן לְשֵׁרוּת שֶׁלִּי? עַ"יְ הַבְּכוֹרוֹת זָכִיתִי בָהֶם וּלְקַחְתִּים תְּמוּרָתָם. לְפִי שֶׁהָיְתָה הָעֲבוֹדָה בַּבְּכוֹרוֹת, וּכְשֶׁחָטְאוּ בָעֵגֶל נִפְסְלוּ, וְהַלְוִיִּם שֶׁלֹּא עָבְדוּ עֲ"זָ נִבְחֲרוּ תַחְתֵּיהֶם (עי' זבחים קי"ב): ואני הנה לקחתי AND I, BEHOLD I HAVE TAKEN [THE LEVITES FROM AMONG THE CHILDREN OF ISRAEL] — This means: And I — whence do “I” claim the right on them from among the children of Israel, that the Israelites should have to hire them (cf. Rashi on v. 8) for My service? It is through the firstborn — to whom I surely have a title — that I have a claim on them (the Levites) and so I take them in their (the firstborns’) stead. For originally the service (the priestly functions) was performed by the firstborn, but when they (the Israelites and among them their firstborn too) sinned by worshipping the golden calf they became disqualified, and the Levites who had not worshipped the idol were chosen in their stead (cf. Zevachim 112b).