Why does it say "Lachen"?
Radak: This is Hashem's reply to Tziyon's and Yerushalayim's complaints against Bavel.
Why does it mention "Riv" and "Nekamah"?
Malbim: Riv is for the theft. Nekamah is for the bloodshed.
Why does it say "v'Hacharavti"?
Malbim: In the end Bavel was totally destroyed; it was an eternal mound (of debris).
What is "Yamah"?
Radak: It is a metaphor for its abundant good, like the water of the sea.
The only other verse that says Mekorah is "Es Mekorah He'erah" (Vayikra 20:18). What is the significance of this?
Ba'al ha'Turim: They received the same punishment - "v'Hovashti Es Mekorah" is like "Aririm Yihyu" (Vayikra 20:21); they will not give birth.