וְנָתַתָּה֙ אֶת־הַלְוִיִּ֔ם לְאַהֲרֹ֖ן וּלְבָנָ֑יו נְתוּנִ֨ם נְתוּנִ֥ם הֵ֙מָּה֙ ל֔וֹ מֵאֵ֖ת בְּנֵ֥י יִשְׂרָאֵֽל׃
And thou shalt give the Levites unto Aaron and to his sons; they are wholly given unto him from the children of Israel.
Sforno on Numbers
נתונים נתונים המה לו, all their (the Levites’) service was to be performed at the instruction of Aaron, to whom the Levites had been delegated by the people.
Rashbam on Numbers
נתונים,נתונים, the repetition of the word is similar to the repetition נתן תתן להם אחזת נחלה, “be sure to give” in English, in Numbers 27,7.