Yahweh uses this question to emphasize that he is the one who caused this ruler from the east to be victorious. Alternate translation: "I am the one who called this powerful ruler from the east and put him in my good service." (See: [[rc://en/ta/man/jit/figs-rquestion]])
Turning them to dust and stubble is a metaphor or exaggeration for completely destroying everything the people of these nations have made. The armies of one from the east will conquer these nations and scatter the people easily. (See: [[rc://en/ta/man/jit/figs-metaphor]] and [[rc://en/ta/man/jit/figs-simile]] and [[rc://en/ta/man/jit/figs-hyperbole]])