1)
Why does it say "Al Ken"?
1.
Radak: Since this comes from Hashem, there is no strategy to be saved.
2.
Malbim: Because the plundering will be from Shakai, all hands will slacken [from preparing needs of war]; because the day is close, every heart will melt due to sudden fear.
2)
Whose hands will soften?
1.
Rashi: Bavel's.
3)
What will be the consequence of the hearts melting?
1.
Radak: They will not find any strength or courage, for it is in the heart - "v'Amitz Libo ba'Giborim" (Amos 2:16).