1)
Why did he need to tell them this?
1.
Metzudas David: Now he returns to tell the story. He did not say this to the people.
2.
Malbim: Until now, only half of Nechemyah's youths and servants held weapons and did not work; everyone else worked. Now they are spread out. It is not enough that workers hold weapons. Now, half of the nation held spears and did not work. They were stationed densely around the entire wall, ready to fight the enemy.
2)
What do we learn from "va'Anachnu Osim ba'Melachah... me'Alos ha'Shachar Ad Tzeis ha'Kochavim"?
1.
Berachos 2b: This is a support that day is from dawn until Tzeis ha'Kochavim. (People normally work from dawn until nightfall.)
