Why does it say "veha'Nevu'ah Oded ha'Navi"?
Radak #1: What should be written next to "veha'Nevu'ah" is omitted. It is as if it says veha'Nevu'ah Nevu'as Oded ha'Navi. Also "ha'Aron ha'Bris" (Yehoshua 3:14, is as if it says ha'Aron Aron ha'Bris).
Radak #2: It is as if it says veha'Nevu'ah l'Oded ha'Navi.
The Nevu'ah was to Azaryah ben Oded (verse 1). Why does it say Oded?
Radak #1: It means Ben Oded, just like "Chanam'el Dodi" (Yirmeyah 32:12). He was Ben Dodi (ibid. 8, 9), even though I gave another Perush there 1 .
Radak #2: Perhaps Oded had such a Nevu'ah about Asa, earlier or at the same time, for he was still alive. We find that he was alive in the days of Achaz (28:9).
Malbim: It has two meanings. (a) The Nevu'ah of Ben Oded. (b) This Nevu'ah was with very strong Ru'ach ha'Kodesh, to the point that the Navi was strengthened - "va'Anachnu Kamnu va'Nis'odad" (Tehilim 20:9). Oded is a Po'el Yotzei (it acts on another, i.e. the Navi). It is a sign that the Nevu'ah was complete.
Radak (Yirmeyah 32:12): Also "Lot Achiv" (Bereishis 14:16) means Ben Achiv. Alternatively, Yirmeyah had a cousin Chanam'el, and also an uncle Chanam'el.
Why did he eradicate the idols now?
Radak: When Asa heard these words, and [Azaryah's] father's Nevu'ah at another time, he was strengthened and eradicated them.
Malbim: From hearing these words, he realized that he needed to finish what he did not yet do.
Why does it say "u'Min he'Arim"?
Malbim: He had not yet eradicated idolatry [from the cities he captured] at all.
How was he Mechadesh the Mizbe'ach?
Gra: He plated it, like regarding Korach "va'Yrak'um Tzipuy la'Mizbe'ach" (Bamidbar 17:4).
