Radak: [The humble] will rejoice when they see the tyrants, scoffers and sinners punished - "uva'Avod Resha'im Rinah" (Mishlei 11:10). Before, they were unable to speak in front of them or rebuke them.

Malbim: Until now, three matters caused the nation to stumble - the deaf did not hear the words of the Sefer, and the humble did not rejoice in Hashem. (a) Tyrants ruled with force, and impeded Avodas Hashem - they ceased. (b) Scoffers enticed the nation with scoffing - they ceased. (c) Open sinners taught people to do like themselves - they were cut off.

Rashi: They are diligent and contemplate how to sin.

Radak: They engage in sin and are quick to sin, and always intend how to execute it.

Malbim: They are people who sin in public.