Also the previous verse said that he will build Heichal Hashem. Why is this repeated?
Radak: It is to strengthen the matter.
Malbim: The previous verse taught that Zerubavel will build Bayis Sheni. Our verse teaches that Melech ha'Mashi'ach will build Bayis Shelishi, and he will bear Hod Hashem.
What beauty will he bear?
Rashi: The beauty of kingship.
Why does it say "v'Yashav u'Mashal Al Kis'o"?
Radak: He will be like a king, who sits on his throne and rules in the land.
Malbim #1: Ha'Mashi'ach will sit and rule, but not Zerubavel, who was under the authority of Malchei Paras. He was submissive, and did not sit on a throne.
Malbim #2: Mashi'ach will sit on Kisei Hashem.
Why does it say "v'Hayah Chohen Al Kis'o"?
Rashi: The Kohen Gadol will sit on the throne of Kehunah. "V'Yashav" applies also to this.
Radak: The Kohen will be in front of [the king's] throne, like "me'Hisyatzev Al Adon Kol ha'Aretz" (5), "v'His'halech Lifnei Meshichi Kol ha'Yamim" (Shmuel I, 2:35). The Kohen comes in front of the king to teach him and to talk with him. The king comes in front of the Kohen Gadol only when he asks the Urim v'Tumim - "v'Lifnei Elazar ha'Kohen Ya'amod v'Sha'al Lo b'Mishpat ha'Urim Lifnei Hashem" (Bamidbar 27:21).
Malbim: Then, the Kohen will be on the chair proper for him; now, he is not.
What will be "Atzas Shalom"?
Rashi: The king and Navi will love each other.
Radak: They will not envy each other. Both will agree about what they do.
Malbim: Now there is not Shalom between the one who sits on the chair of conduct and the Kohen. In the days of the Chashmona'im, they wore the crown of kingship and attributed grandeur to themselves. Afterwards, the kingship lowered the crown of Kehunah - they sold [appointment to be Kohen Gadol] for money, and it was lowly in their eyes. In the future, each will sit on his throne in Shalom.
