1)
What is the meaning of "Nachah Shaktah Kol ha'Aretz"?
1.
Shabbos 149b: This implies that during his life, no one rejoiced.
2.
Radak: When Nebuchadnetzar's grandson died, and his regime ended, the entire land was serene.
3.
Malbim: The verse depicts that the entire land already had respite, and forgot all that this tyrant did to it.
2)
What did they sing?
1.
Rashi: "Nachah Shaktah Kol ha'Aretz."
