Therefore he knoweth their works, and he overturneth them in the night, so that they are destroyed.
Therefore - because He knows all things (Job 34:21), He knows their works, without a formal investigation (Job 34:24).
In the night - suddenly, unexpectedly (Job 34:20). Fitly in the night, as it was in it that the godless hid themselves (Job 34:22). Umbreit, less simply, for "over-turneth" х haapak (H2015)], translates, 'walketh' - i:e., God is ever on the alert, discovering all wickedness.