Commentary for Numbers 4:27

על פי אהרן ובניו AT THE APPOINTMENT OF AARON AND HIS SONS [SHALL BE ALL THE SERVICE OF THE SONS OF THE GERSHONITES] — and which of his sons shall be appointed over them? Everything was (v. 28) “under the hand of Ithamar the son of Aaron the priest”.

AT THE COMMANDMENT OF AARON AND HIS SONS SHALL BE ALL THE SERVICE OF THE SONS OF THE GERSHONITES — “and which of Aaron’s sons shall be appointed over them? Ithamar” [as is stated in the following verse]. This is Rashi’s language. But it is not correct for [if only Ithamar was appointed], why mention Aaron [at all — at the commandment of Aaron etc.]? Rather, the meaning of [the expression] at the commandment of Aaron and his sons shall be all the service is that the services of the Gershonites shall be at their command. They are to appoint the Gershonites to their work, saying: “This particular Gershonite shall be the overseer for such-and-such a matter” — “This one shall sing [at the services] in such-and-such a way, or attend to the gates³See further Note 31. and for Scriptural basis see my translation of Sefer Hamitzvoth (“The Commandments,” Vol. I, pp. 32-33). in a certain manner, or shall carry a certain number of the curtains.” At the time of journeying they were also not permitted to dismantle the Tabernacle or to begin loading it until Aaron and his sons commanded them to do so. Thus all of them [Aaron and his sons] were needed for the appointed charge, Eleazar being the chief over the three princes [of the three main families of the Levites],⁴See in Seder Bamidbar Note 204. and Ithamar being the overseer over the sons of Gershon⁵Verse 28. and Merari.⁶Verse 33.
Scripture states and ‘ye’ shall appoint unto them in charge [all which they have to carry]⁷Verse 27. because Moses was to be with them at the time of the appointments, when the charges were given to them; but their charge shall be under the hand of Ithamar,⁵Verse 28. meaning that each one was to return the vessels to his control when the Tabernacle came to rest, saying to him: “Here you have the vessels that were handed over to me.”

לכל משאם, at the time of the journey,