Rashi on TanakhPsalms 96

a new song This song deals with the future, as is proven by the final verse, “for He has come to judge the earth.” Any reference to a “new song” deals with the future.

Ascribe to the Lord, families of peoples And what shall you ascribe to Him? Ascribe to the Lord glory and might.

“The Lord has reigned” This song will be [sung] in the future.

He will judge peoples with equity Those whom he will turn into a clear tongue (Zeph. 3:9).

with equity with merits.

the sea...will roar to raise its voice in praise.

all the forest trees All the rulers of the nations.