Radak: It is about the gathering of exiles of Yisrael. Then, they will say that the entire land will shout to Hashem, for they will see the wonders that He did for Yisrael.

Malbim: The author's name is not mentioned. I say that it was Menasheh ben Chizkiyah. After Hashem afflicted him, he repented; "u'Sefilaso v'He'aser Lo