Radak on Psalms
So shall all those that put their trust in Thee rejoice; They shall ever ring out their joy – just the opposite of the enemies, who do not trust in Thee; and when Thou shalt thrust them out those who trust in Thee shall rejoice. And the sense of
Rashi on Psalms
exult in You when they see that You bless the righteous man, Jacob, and his seed.