במדבר, פרק א׳, פסוק ט׳

The appointment of Eliab son of Helon as the leader of the tribe of Zebulun marks a distinct milestone in the organization of the Israelites. His selection serves to complete a specific section of the nation's leadership roster.

With his appointment, the list of leaders representing the tribes descended from Leah's six sons is brought to a close. In establishing this leadership structure, these specific tribes are organized strictly according to the natural birth order of the brothers [ביאור שטיינזלץ].