What does "Nesunim lo" mean?
Rashi: It means that they are charged to assist Aharon in the Avodah. 1
Seforno: Refer to 3:9:2:2.
See Sifsei Chachamim.
Why does the Torah repeat the word "Nesunim"?
Rashbam: It is simply a double Lashon (perhaps for emphasis), in the way that the Torah sometimes does.
Seforno: It teaches us that all the Avodah of the Levi'im was according to the instructions of Aharon and his sons, and nobody else.
And what are the implications of Me'eis b'nei Yisrael?