Why did Judah lead instead of Reuben, the firstborn?
Reuben was the firstborn and should have held leadership, but he sinned through immorality with his father’s wife or concubine, so God in His sovereignty gave that place to Judah. Christ also comes from Judah, and Scripture says the scepter shall never leave Judah.
Les explains that Reuben was the oldest and should have been in the lead position, but because he sinned—he was immoral, having a relationship with his father’s wife or concubine—God in His sovereignty brought Judah to the place Reuben should have enjoyed. Judah therefore took leadership. Les also points out another reason: Christ comes out of the tribe of Judah, and it says the scepter shall never leave Judah. In the camp arrangement, the east side included Judah, Issachar, and Zebulun, and Judah was always the tribe that led whenever they journeyed.