Yahweh speaks of testing the people and dealing with their evil ways, as if they were metal that he were melting in a crucible to remove its impurities. (See: [[rc://en/ta/man/jit/figs-metaphor]])
Yahweh uses this rhetorical question to state that this is how he needs to deal with his people because of what they have done. This question can be written as a statement. Alternate translation: "for this is how I must deal with my people because of what they have done." (See: [[rc://en/ta/man/jit/figs-rquestion]])