How was he "Atzur"?
Rashi: They found him in his house.
Ibn Ezra: He was confined in front of the Creator to serve Him, like one who confines himself in a fast, like Do'eg ha'Edomi, who was Ne'etzar.
Malbim: He was ill, and could not leave his house, so Nechemyah needed to go to him.
Why did he say "Niva'ed... [v'Laylah Ba'im]"?
Rashi: Shemayah was a false Nevi'im. Sanvalat and his friends bribed him to scare Nechemyah, in order to cease the work.
Malbim: This was not part of the Nevu'ah. Rather, he said that he heard from spies that Tzarei Yehudah are coming to kill him that night.
Who comes to kill you?
Rashi: Sanvalat and his friends.
Malbim: Tzarei Yehudah.
Why did he tell him to enter the Heichal?
Rashi: You can close the doors of the Heichal. There were not yet doors on the gates of the city, like it said above (1). Malbim - he suggested that he and Nechemyah will go there to take refuge.
