Why does it say "v'Yad'u
Radak: Then this nation will know that I said Emes to them. When the punishment first came, they did not realize that it was due to their sin. They said, if evil came to us now, twice as much good will come to us.
Malbim: Then this nation will know that what they said [were vain words].
Why does it mention Efrayim and Shomron?
Malbim: Efrayim is the country, and Shomron is the capitol.
What is the meaning of "b'Ga'avah uv'Godel Levav Leimor"?
Rashi: What they said with haughtiness.
Radak: When Hashem's word comes on them, they will be finished and exiled from their land. They they will know that what they said (refer to 9:8:1:1) was with haughtiness; it was vain consolation. Then, their pride will cease.
Malbim: Amidst haughtiness, they relied on what everyone said (brought in verse 9).
