Why should they sing to Hashem?
Radak: His great acts will be known in the entire land.
Malbim: Because he did Ge'us, i.e. rising from natural conduct to miraculous conduct.
What Ge'us did Hashem do?
Radak: This is like it says about Keri'as Yam Suf, "Ki Ga'o Ga'ah" (Shemos 15:1).
Malbim: Refer to 12:5:1:2.
Why does it say "Muda'as Zos b'Chol ha'Aretz"?
Radak: It will be known in the entire land that He took a poor nation out of many awesome nations. Also the plague (sudden death) of Gog and Magog will be in the entire land. Therefore, you should sing to Him!
Malbim: This is unlike previous miracles that were publicized only among Yisrael, but not in the entire settled world. Now, also the nations will see wonders.
