Why does the Torah repeat the word "Nesunim"?
Rashi: Because the Levi'im were designated for Hashem as regards carrying and as regards singing. 1
Seforno: The first "Nesunim" refers to their volunteering to serve Hashem 2 and the second, to the fact that they were given to Hashem from the rest of Yisrael, who became obligated to sustain them with Ma'aser Rishon.
Oznayim la'Torah: The Torah divides the Avodas ha'Levi'im into two groups - carrying, which was confined to the era of the desert, and singing, which would apply in the Beis-Hamikdash as well (In that case, it seems that one "Nesunim" pertains to carrying, and the other, to singing and carrying - which also applied in the Beis-Hamikdash).
