Praise the Lord! Sing to the Lord a new song... Let Israel be glad in its Maker.
The praise is to be by dancing and by playing the tambourine and lyre.
A reason is given--the Lord gives victory to the humble. They respond by singing.
The mood of the psalm shifts. These singers are holding swords so that they can wreak vengeance and punishment on their enemies. Executing judgment on their rulers is glory for his faithful ones.
The psalm ends as it began: Praise the Lord!
Why would these angry, vengeful verses be included in the Psalter? Are they appropriate for worship? Are they appropriate for private devotion?
The notes in the New Interpreter's Study Bible points out that since Israel would never have been in position to take kings and princes captive, the rhetoric is exaggerated. Yet, even if they were incapable of humiliating the powerful nations that attacked them, they did have hope for their own survival. The Lord could and would vindicate the righteous and impose judgment on their enemies.
Transferring the message of this psalm to our time could mean for us questioning who are the weak and humble now and who are the powerful.