Comentário sobre Números 4:21

-22. וידבר ה׳…נשא, G'd said to Moses: "Take the sum, etc." The Torah had to repeat the line וידבר ה׳ אל משה although it had used this introduction when telling Moses to count the Kehatites. The reason is that in this instance the Torah added the instruction to elevate the status of the clan of Gershon in relation to that of the clan of Merari. The elevation of the clan of Gershon was not of the same nature as that of the Kehatites as compared to the clan of Gershon. The former were distinguished in that they carried the Holy Ark. We would not have known that the clan of Gershon were more distinguished than the clan of Merari had the Torah not employed the term נשא in respect to their tasks. The Torah makes this even clearer when it does not preface the instruction detailing the tasks of the clan of Merari by G'd giving Moses a separate command (compare verse 29). The Torah contents itself with telling Moses to count (תפקד) the members of that clan before detailing their tasks.

אל משה, to Moses. Interestingly, when the count is actually being performed (verse 34) the Torah reports that both Moses and Aaron did the counting. This was because already in 4,1 G'd had commanded both Moses and Aaron to do the counting. G'd included Aaron in the commandment to instruct the Kehatites to be very careful so that they would not incur death seeing Aaron himself was liable to death if he entered the Holy of Holies, the site where the Holy Ark was situated in an unauthorised fashion at an unauthorised time. There was no need to include Aaron then in the command to assign the tasks of the clan of Gershon or of Merari.