This phrase refers to the punishment that will happen as a result of Yahweh's decree. Alternate translation: "before Yahweh punishes you" (See: [[rc://en/ta/man/jit/figs-metonymy]])
The chaff is the insignificant part of the plant that the wind blows away. In a similar way, the day of judgment will pass quickly. Alternate translation: "that day passes as quickly as chaff blown by the wind" (See: [[rc://en/ta/man/jit/figs-simile]])
The prophet repeats the same phrase almost exactly in order to emphasize how terrible Yahweh's judgment will be and the urgency with which the people must repent. (See: [[rc://en/ta/man/jit/figs-parallelism]])