Therefore he knoweth their works - Or, "Because he knoweth their works." The word (לכן lākên) here rendered "therefore" is evidently used as denoting that since or because he was intimately acquainted with all which they did, he could justly bring vengeance upon them without long investigation.
And he overturneth them in the night - literally, "he turneth night;" meaning, probably, he turns night upon them; that is, he brings calamity upon them. The word "night" is often used to denote calamity, or ruin. Umbreit understands it in the sense of "turning about the night;" that is, that they had covered up their deeds as in the night, but that God "so turns the night about" as to bring them to the light of day. The Vulgate renders it "et ideireo inducit noctem," "and therefore he brings night;" that is, he brings adversity and ruin. This is probably the correct interpretation.
So that they are destroyed - Margin, "crushed." The idea is, that when God thus brings adversity upon them, they are prostrated beneath his power.

He knoweth their works - He knows what they have done, and what they are plotting to do.
He overturneth them in the night - In the revolution of a single night the plenitude of power on which the day closed is annihilated. See the cases of Belshazzar and Babylon.

Therefore he knoweth their (s) works, and he overturneth [them] in the (t) night, so that they are destroyed.
(s) Make it known that they are wicked.
(t) Declare the things that were hid.

Therefore he knoweth their works,.... Being God omniscient, or rather takes notice of them, weighs and considers them, and gives to man according to them; or rather makes them known, for of his omniscience Elihu had spoken before; he makes them known to themselves, fastens convictions of their evil ways and works on their consciences, and obliges them to confess them, as the instances of Cain, Pharaoh, and others, show; and he makes them known to others by the judgment he executes, as on the old world, Sodom and Gomorrah; and the works of all will be made manifest at the day of judgment;
and he overturneth them in the night; literally taken, as the firstborn of the Egyptians were slain in the night, Exodus 12:30; and Pharaoh and his host were drowned in the Red sea in the night, Exodus 15:4; and the Assyrian army were destroyed by an angel in one night, 2-Kings 19:35; and Belshazzar was killed in the night, and the Babylonian empire translated to the Medes and Persians at the same time, Daniel 5:30, or figuratively, that is, suddenly, at unawares, and by surprise, and as quickly and easily as the night is turned into day; and such a revolution is made, as when he turns the night into day, and discovers and makes known all their secret actions committed in the dark; or he turns the night of calamity upon them, and puts an end to their light of temporal happiness and prosperity; or turns the night of death and everlasting wrath and justice on them, the blackness of darkness upon them:
so that they are destroyed; both in a temporal sense, on every side, with an utter destruction; and in a spiritual sense, with an everlasting one.

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 "overturneth," translates, "walketh"; that is, God is ever on the alert, discovering all wickedness.