If the scourge slay suddenly - If calamity comes in a sudden and unexpected manner. Dr. Good, following Reiske, translates this,” if he suddenly slay the oppressor,” understanding the word scourge שׁוט shôṭ as meaning an oppressor, or one whom God employs as a scourge of nations. But this is contrary to all the ancient versions. The word שׁוט shôṭ means properly a whip, a scourge (compare the notes at Job 5:21), and then calamity or affliction sent by God upon men. Such is clearly the case here.
He will laugh at the trial of the innocent - That is, he seems to disregard or to be pleased with their trials. He does not interpose to rescue them. He seems to look calmly on, and suffers them to be overwhelmed with others. This is a poetic expression, and cannot mean that God derides the trials of the innocent, or mocks their sufferings. It means that he seems to be inattentive to them; he suffers the righteous and the wicked to be swept away together as if he were regardless of character.