Why does Hashem rebuke the Satan?
Radak: The angel rebuked him; the angel is called on the name of his Master. We find like this with Gid'on and in other places.
Malbim: Hashem is the Master of mercy. He leans to vindicate His creations.
Malbim (7): Even though this Nevu'ah was for Yehoshua himself, it also included his future seed. They will be called on his name. The Navi saw that sometimes they will be judged, and the Satan will prosecute that they should be burned, i.e. at the time of Shmad (decrees against Mitzvos) in the days of Antiyochas, who wanted to eradicate the Kohanim. Hashem rebuked the Satan.
Why does it add "va'Yig'ar Hashem"?
Radak: This refers to Hashem. (Above, it referred to an angel.)
Malbim: This is a second reason to rebuke the Satan. Refer to 3:2:3:3.
Why does it add "ha'Bocher bi'Yrushalayim"?
Rashi: Hashem chose Yerushalayim, that you will not enter in front of Him to prosecute against this Tzadik.
Radak: Hashem chose to build Yerushalayim ? you cannot prosecute against it!
Malbim: Hashem chooses Yerushalayim; the Kohen Gadol's ancestors served in the Mikdash. Due to this, it was decided that he be saved via a miracle.
Why does it say "ha'Lo Zeh Ud Mutzal me'Esh"?
Rashi: He was proper ? therefore he was saved from burning in the fire. It says in Sanhedrin 93a that he was cast in a fire with Achav ben Kolayah and Achav's friend (another false Navi, Tzidkiyahu). Radak ? they were burned, and Yehoshua was saved.
Radak: He is like a burning spit, that they remove it from the fire lest it burn more. So he was saved from the fire of Galus to come to Yerushalayim, build the Bayis and serve in it as Kohen.
Malbim: Even though he was not worthy of a miracle like Chananyah, Misha'el and Azaryah ? the fire did not affect even their garments ? Yehoshua's garments were burned. He is like a spit that the fire singed. In any case he was saved.
Malbim (7): Yehoshua will be like a spit removed from the fire, like in the days of the Chashmona'im; they were saved via a miracle and Hashem's Hashgachah.
