Yahweh is using this question to rebuke those who make idols. This question can be translated as a statement. Alternate translation: "Only fools would form a god or cast an idol that is worthless." (See: [[rc://en/ta/man/jit/figs-rquestion]])
The word "worthless" does not distinguish worthless idols from idols that have worth, because all idols are worthless. Alternate translation: "cast worthless idols" (See: [[rc://en/ta/man/jit/figs-distinguish]])