Radak: It is an expression of Aveilus (Malbim - that no one enters or leaves). It is a metaphor, like "Kol She'areha Shomemim" (Eichah 1:4).
2.
Malbim: The custom of early nations was not to mourn over a Gibor who died in war, lest it soften the nation's heart. Just the contrary, they celebrated the day of his death, for he acquired an eternal name. Here, all the Giborim will perish. The widows will sit alone; their doors "v'Anu v'Avlu" - no one enters to visit them.
3)
What are "Pesacheha"?
1.
Rashi: The gates of your cities and houses. There will be eulogies in all your gates.
4)
What is the meaning of "v'Nikasah"?
1.
Rashi: It will be totally emptied, like "v'Gam Ani Nasati Lachem Nikyon Shinayim" (Amos 4:6); 'Ploni came out Naki from his property' (Bava Kama 41a).
2.
Radak: It will be emptied of its residents.
3.
Malbim #1: It will be emptied of all that was in it.
4.
Malbim #2: The custom was that if a Gibor died in war, they would punish his widow or relatives if they mourned him, lest it soften the nation's heart. She will be exempt from punishment if "she sits on the ground", for no one will know. [Also], the nation already lost all hope.
5)
What will sit on the ground?
1.
Radak #1: Tziyon will be destroyed; its walls, houses and towers will fall to the ground.
2.
Radak #2: This is a metaphor for mourning, as if the city sits on the ground mourning the loss of its people - "Yeshvu la'Aretz Yidemu Ziknei Vas Tziyon" (Eichah 2:10).
3.
Malbim: The widow will be able to sit on the ground [without punishment - refer to 3:26:4:4].
