Who is Maroz?
Rashi citing Mo'ed Katan 16a #1: It is a star.
Rashi citing Mo'ed Katan 16a #2: It is an important man. He was near the war, and did not come to the war.
Mahari Kara: Some say that it is people of the city Maroz. It seems that they are correct, for its residents are cursed.
Radak: It is a nearby city, and it did not come to help. She did not curse the far cities that did not come.
Malbim: It was a city of mighty men.
Who is the Malach?
Rashi: It is Barak; he was Hashem's Shali'ach (Targum Yonasan - His Navi).
Radak: It is an angel; Devorah said so via prophecy.
What is the meaning of "Yoshveha"?
Rashi: It is one who sits within four Amos of him. [This is forbidden, for] Barak excommunicated him (Mo'ed Katan 16a).
Malbim: They are its residents who sat there, and did not come b'Giborim, i.e. with its Giborim.
What is the meaning of "l'Ezras Hashem"?
Rashi: One who helps Yisrael, it is as if helps the Shechinah!
