במדבר, פרק ד׳, פסוק כ״ח

The daily operations of the Tabernacle required a highly organized chain of command and clear boundaries of responsibility among the working families. The duties assigned to the Gershonite families were entirely exclusive to them. Members of the Kohath and Merari families were strictly forbidden from touching their items or interfering with their assigned tasks [מלבי״ם].

To maintain this strict order, the Gershonites carried out their work under the direct command of Ithamar, the second of Aaron the priest's remaining sons [ביאור שטיינזלץ]. Ithamar's authority functioned on multiple practical levels. He was personally responsible for handing over the exact loads to the Gershonites [שד״ל]. Additionally, he acted as the chief guard, making sure that every single object was carefully placed in its proper location [העמק דבר]. Even though each individual Gershonite had a permanent assignment and a fixed shift to carry a specific item, Ithamar served as the highest supervisor, watching over them to ensure they performed their duties faithfully [מלבי״ם].

Placing Ithamar in this leadership role marked a new, permanent phase in the service of the Tabernacle. While the initial training and introduction of the Gershonites into their positions were handled by Aaron and all his sons together, the ongoing, daily supervision was now handed over exclusively to Ithamar [רש״ר הירש].