Radak: Even the nations should blow Teru'ah and rejoice over the salvation of Yisrael, for in their salvation will be the salvation of the entire world; there will not be more wars between nations.

Malbim: Normally, when the king is closed in his palace, the nation sings for his honor with musical accompaniment and harps. When he leaves his palace and appears to the people, they sound a great Teru'ah. This is a sign that their king is among them, like I explained above (95:1). Here the verse depicts Yeshu'as Hashem as an entity, as if Hashem appears to the world in His honor, therefore the entire world blows Teru'ah, for He came among them, and afterwards they sing of His praises and constant deeds. It adds ¹ that it will always be so.

Radak: Pischu (begin) singing.