What will be soon?
Rashi: In a few days - it is easy in My eyes if you will repent to Me.
Radak: You will see how I will reverse you. Me'at Miz'ar repeats the matter in different words, to diminish the time. This Nevu'ah was said in the days of Achaz; it was fulfilled shortly after, in the days of Chizkiyah.
Why does it say "v'Shav Levanon"?
Rashi: Levanon is a tree forest 1 . It will become like Karmel - a settlement of fields and vineyards.
Rashi (on Bereishis Rabah 24:1): Karmel is bigger than Levanon, and Ya'ar is bigger than Karmel.
Malbim: Levanon is full of barren trees. This is a metaphor for Resha'im. It will become like Karmel, and bear Kodesh fruits and good deeds.
Radak: It is Ya'ar ha'Levanon. It has tall cedars. Karmel is grain fields, vineyards and low trees. This is a metaphor for the haughty people in the days of Achaz. They will be lowered in the days of Chizkiyah, and will not be allowed to speak. They will be forced to repent.
Why will Karmel be considered a forest?
Rashi citing Targum Yonasan: Many cities will dwell [there].
Rashi (from Bereishis Rabah 24:1): Forests of people will inhabit cities - people as dense as a forest, which is full of trees.
Rashi (on Bereishis Rabah 24:1) #1: Refer to 29:17:2:2.
Rashi (on Bereishis Rabah 24:1) #2: People will multiply in the world like Chayos (alternatively - trees) in the forest, if they will publicize their deeds and repent.
Radak: The low, humble people in the days of Achaz, who were unable to rebuke [the proud], in the days of Chizkiyah they will be elevated like cedars of the Levanon forest. They will increase in honor and grandeur until they will resemble cedars of Levanon - "v'Yasfu Anavim ba'Shem Simchah" (19).
Malbim: The shortcoming of Karmel is that it is soft and weak. It will be strong like the forest. I.e. the Tzadikim will be strong and powerful.
