Albert Barnes Commentary Psalms 94:4

"They prate, they speak arrogantly: All the workers of iniquity boast themselves." — Psalms 94:4 (ASV)

How long shall they utter and speak hard things? - The word rendered 'utter' means to pour forth—as water from a fountain; to pour forth copiously. The meaning is, that they seemed to be full, and that they poured forth evil words as a fountain pours forth water. The phrase “hard things” means proud, unfeeling, insolent things; things which are unjust, unkind, severe, harsh.

And all the workers of iniquity boast themselves? - Boast of their power and their success. How long shall they be permitted to have such success as may seem to justify them in their exultation?