It says that Bnei Kehas were counted "Al Pi Hashem b'Yad Moshe", and also Bnei Merari (verse 45). Why does it say about Bnei Gershon only "Al Pi Hashem" (verse 41)?
Da'as Zekeinim, Rosh, Hadar Zekeinim (22): Hashem commanded Moshe and Aharon to count Kehas (verse 1), so it says here b'Yad Moshe to teach that Moshe was primary. It does not say before the command to count Merari that Hashem commanded it, so afterwards the Torah teaches that He commanded Moshe. Regarding Gershon, Hashem commanded Moshe, so it need not say afterwards "b'Yad Moshe."