1. Exposition

Why is mention made of Judah and Benjamin?

Ezra 10:9 (ESV)

9 Then all the men of Judah and Benjamin assembled at Jerusalem within the three days. It was the ninth month, on the twentieth day of the month. And all the people sat in the open square before the house of God, trembling because of this matter and because of the heavy rain.

Since it was people from the southern kingdom who were taken off into exile by the Babylonians, most of those who returned were also from the southern kingdom. The southern kingdom was made up the two tribes of Judah and Benjamin.