Why is it improper that we are sitting?
Radak: We dwell in villages and open cities as if we are secure. What help do we have?!
Malbim: We should be preparing counsel and Gevurah for war. We should go to the fortified cities to fight the enemy.
What is the meaning of "v'Nidmah Sham"?
Rashi: We will sit there silently and mourn. Radak - we cannot complain about the affliction coming on us. Hashem made us silent, for we sinned against Him.
Malbim: The Navi answers, we will not do anything in the fortified cities, for Hashem made us silent, like mourners.
What is the root of "v'Nidmah"?
Radak #1: The root is Damam. This is a Kal conjugation, like "Yisom v'Yishrok" (19:8), "Mah Ekov" (Bamidbar 23:8), "Yidmu ka'Aven" (Shemos 15:16).
Radak citing his father: The root is Nadam. The root of Hadimanu (later in this verse) is Damam. It is Hif'il. The Hei has Chataf Patach; Hashem made us silent, i.e. we may not complain, for we sinned against Him. How can we be brazen against Him [to complain]?!
Radak #2: It is cutting off, like "Yidemu li'Sh'ol" (Tehilim 31:18), "v'Nadamu Ne'os ha'Shalom" (below, 25:37).
What is "Mei Rosh"?
Rashi citing Targum Yonasan: A cup of evil anger, like Rosh ha'Peten (a viper's head), i.e. the venom in its teeth. Radak (9:14) - most [poison] is made from this. Malbim - this is in place of the cup of consolation normally given to mourners.
Radak: It is poison squeezed from an herb [called Rosh]; this is why it says "Mei". The Navi speaks b'Leshon Yisrael.
